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GIS (Geographic Information Systems)

Start here for general GIS questions.

ArcGIS Desktop (ArcMap) Tutorials

Learning how to effectively use the ArcGIS Desktop application to view or edit data, perform spatial analysis, or create maps and figures can seem like a daunting task.  The ArcGIS software is highly functional, spatial data can come in a wide variety of formats, and sometimes even simple tasks like viewing data and creating a simple map can involve multiple steps. The tutorial pages compiled here are intended to provide discrete skills so that you can quickly find the steps required to complete some of the more common tasks encountered when working with spatial data.  Each tab includes the steps necessary to perform the listed task along with links at the bottom to additional online resources.  If you find these resources helpful or if you have suggestions for new tutorials, please let us know.  For instructions on installing ArcMap on your own machine, see the Software Installation Guide.

The tutorials on this page are designed to build skills incrementally following a standard progression (suggested order is shown in the tab numbering) or specific content may be viewed to help you master a particular task.

Other resources are available online to learn how to use the ArcMap software:

  • Getting Started With ArcMap - learn how to use ArcMap and GIS to map deforestation in the rainforest
  • Learn ArcGIS - this page features many tutorials, select those that are designed for the application that you are using
    • Some lessons at this site require you to be a member of the WashU ArcGIS Online Organization
    • See this page to create an account using your WUSTL Key credentials

Getting to Know the ArcMap Window

The ArcMap application window gives you access to menus, tools, and allows you to visualize and mange data. The diagram below highlights the major components of the window and defines the areas that will be referred to in the tutorial pages.  

 

 

 

 

 

 

 

 

 

 

 

 

 

The menus and toolbars give access to frequently used functions and tools.  Several other special purpose toolbars can be added by right clicking in the white space on the top bar and selecting the toolbar of interest from the complete list.  Tabbed windows expand when clicked and can be locked in place for extended usage.  Data is added to the map and appears in the Data Frame and as an entry in the Table of Contents.

Additional Resources

Accessing Data and Adding it to ArcMap

This tutorial was created using ArcMap 10.6. Instructions may vary slightly for different versions of the application. 

There are several ways to access data within ArcMap.  This tutorial covers:


Adding Data From Your Local Machine

In order to add data to ArcMap, a 'Folder Connection' must exist.  A 'Folder Connection' creates a persistent link to a location on your local machine or to a network location.  For instructions on creating a folder connection, see the Using Folder Connections ArcMap Online Help.  It is recommended to create folder connections at the highest directory level possible to avoid multiple connections to nested folders.

Once a connection has been created to the folder containing the desired data, add data to ArcMap by following the steps below.

1) Click the 'Add Data' button (Located on the Standard toolbar, typically at the top of the application window)

2) Expand 'Folder Connections' and navigate to the connection at the desired location

3) Click on the desired file to select it.  To select multiple files, hold the SHIFT key and click the file names.

4) Click 'Add' to add the selected files to the map window.

Alternatively, you may drag and drop data from the Catalog Pane.  See the next section for step by step instructions.


Adding Data From a Shared Network Drive (WU Geospatial Data Collection)

This example uses the WashU Geospatial Data Collection (formerly known as 'gispublic') as the network share.  

  • See the GIS FAQ page for instructions on requesting access to the network drive.
  • A visual example of creating the necessary 'Folder Connection' in ArcMap is given here.

Adding an Esri Basemap

Base layer data such as imagery, street maps, and topography can be accessed through web-based services from commercial or public sources. One source for ArcGIS users is through ESRI's basemap services.

To add an Esri basemap to your map, click on "File" > “Add Data" > "Add Basemap" or click on the black down arrow next to the Add Data icon and select "Add Basemap".

A browser window will open showing available data layers. Click on the thumbnail of the desired Basemap to add it to your map.  The basemap layer is a link to an online service hosting the data. 

This example shows the Esri Imagery which has been zoomed to show the Brookings Quadrangle. Online services like this one provide seamless datasets covering the entire world at varying levels of detail. Adding such data to your map can provide context for your users with very little effort required: 


Adding a web service from a GIS Server

The “GIS Servers” folder in the “Add Data” window contains wizards that will guide you through the process of connecting to other types of online GIS services. One such service is offered by the Missouri Spatial Data Information Service (MSDIS). MSDIS offers online access to 2 foot resolution aerial images of Missouri, among other raster and vector data layers.

To add a link to an online GIS Server, click on the “Add Data” icon. Select "GIS Servers" from the Catalog listing. A new window will open showing links to wizards that will guide you through the process of adding new connections. 

For example, aerial images of Missouri can be added from MSDIS by selecting "Add ArcGIS Server". Select "Use GIS Services" and click Next.

Enter the Server URL which can be found at MSDIS website http://moimagery.missouri.edu/arcgis/rest/services

Then you can access the data of this service from ArcCatalog under GIS Servers. 

Many agencies offer online GIS services that can enhance your map projects using the method shown above. Use a web search engine to identify appropriate data layers and their format. Select the appropriate connection wizard to establish a link to the dataset and then add the data to your map via the "Add Data" icon or menu.

 

Identifying Feature Data on a Map

Typical GIS data stores more information than the physical shape of geographic features. For example, a county dataset will contain geographic boundaries, but it may also store demographic, or economic data about each county feature. This additional information is called "attributes" and these values can be used to control symbology and labeling. If a dataset is already displayed on a map using ArcMap, using the Identify Tool  is the easiest way to access this information for a specific feature.

Click on the Idenfity tool on the "Tools" toolbar and the mouse icon will change to display an "i" inside a black circle. Select an item on the map by clicking on it with the tool. Be sure to click within a few pixels of the feature; otherwise, it may not be selected. To adjust this sensitivity, go to Selection > Selection Options... and change the Selection Tolerance. The example below shows the counties in Missouri and Franklin county has been selected by the Identify Tool (the county polygon briefly flashes dark green to indicate it was selected) and its attribute values are shown in the "Identify" window that pops up.

 

When a feature or features (hold down ctrl key or click and drag a rectangle to select multiple features) are selected, the Identify window will display their attributes, sorted first by layer then by feature. Using the drop-­down menu, you may control the selectable layers that will respond to the Identify tool.  Features can be 'flashed' in the map view window by clicking on the feature name in the upper part of the Identify window. This function is helpful if, say, a layer of roads and a layer of delivery routes run concurrently and data from only one layer is desired.

 

 

Symbology: Editing Map Symbols and Visualization

The visual representation of features on a map is called symbology. ArcMap displays data using a default 'single symbol' setting such that all features in a given layer will appear with the same color and outline characteristics. The user has the flexibility to control the map symbology of map features based on category or quantity values stored in the dataset's attribute table. Symbology can be chosen from a variety of visual effects, including solid colors or outlined areas for polygons, circles, squares, and other symbols for points, and solid or patterned lines.

   

In ArcMap, the current symbology of a map layer is displayed
 in the table of contents panel. 

To recreate this example:

  • Open ArcMap
  • Add layers from the Home Folder
    • MO_Counties
    • MO_Highways
    • MO_Places

Your map may use different symbology, ArcMap uses default symbology settings when layers are added to a map document.

 

 

 

Notice that all of the layers in the example above are shown by just a single symbol. For single-­symbol layers, symbology settings can be quickly edited simply by clicking on the symbol patch below the layer name in the Table of Contents panel.  This will open the Symbol Selector window, allowing you to quickly change the settings for:

  • Fill color
  • Outline width & color
  • The "Edit Symbol..." button enables access to more characteristics such as symbol type and outline style

 

 

 

 

 

  

 

 

To access the most comprehensive symbology options for any layer (including category or quantity-­based attributes), right-click on the layer name in the Table of Contents, choose Properties, and select the Symbology tab at the top to open this panel. The column on the left allows you to choose whether the layer features should be symbolized by a single symbol (Features), classified by category (Categories) or quantity (Quantities), or labeled with charts (Charts). The "Classify..." button reveals more controls for selecting the classification type such as Manual Breaks, Defined Interval, and Quantiles.

 

 

 

In the example shown below, a layer of county boundaries (MO_Counties) uses color intensity to indicate higher population counts. The MO_Highways and MO_Places layers have been turned off for clarity by 'unchecking' the box to the left of each Layer Name.  The MO_Counties layer contains an attribute storing year 2000 population data from the US Census and this quantity controls the color scheme assigned to each county polygon.

To apply this style of symbology; 

  • Open the Layer's Properties window (right click the MO_Counties layer name and select Properties OR double click the layer name)
  • Access the Symbology tab 
  • Select the Quantities heading, and the Graduated colors option.
    • Use the Value: dropdown menu to specify which attribute field contains the population density data.
    • An optional normalization attribute, number of breaks, and color ramp can be specified as well.
    • As these settings are selected, the symbology is updated in the table.
    • Other ways of symbolizing the layer are specified using similar methods through this window.
  • Once all settings have been completed:
    • Click APPLY to make the changes and leave the Properties window open.
      • This option is useful when you want to evaluate the changes but might make further adjustments.
    • Click OK to make the changes and close the Properties window.

For more information about adding and editing visual elements on maps, see our Creating a Map Layout tutorial.

Additional resources:

Overview of Geographic Coordinate Systems (GCS) and Map Projections

Coordinate systems provide a basis for identifying locations on the earth's surface. Historically, many coordinate systems have been devised, with the oldest ones assuming a flat earth and later based on a perfect sphere. Today's geographic coordinate systems are now based on a cartographic spheroid (an ellipse rotated about its axis) to more closely represent the earth's true shape and surface. Additionally, map projection coordinate systems have been developed to determine how the curved surface of the earth is depicted on a flat map.

A modern Geographic Coordinate System uses latitude and longitude to describe a location. The coordinate system is based on an origin: the intersection of a chosen prime meridian and equator. The coordinate system can pinpoint exact locations, but are not necessarily ideal for computing units of measure since the distance represented by a degree of longitude changes depending on latitude (meridians are closer together farther from the equator, converging to a point at the poles). Additionally, the earth is not a perfect spheroid. The South Pole is actually closer to the equator than the North Pole, and elevations on the surface are varied. Because of these conditions, the center of a coordinate system based on a spheroid is slightly adjusted so that part of the spheroid lines up remarkably well with a portion of the earth's surface. This adjustment is different, depending on what region of the surface is being mapped, so many different datums are used throughout the world.

A second cartographic problem is that flat maps are used to portray an area that is, in reality, a curved surface. Because of this, a map projection has to be defined when drawing a map. Some common projections can be thought of as wrapping a cylinder of paper around the earth so that it is tangent at the equator, or perhaps attaching a plane sheet of paper to the earth at one single point. Numerous map projections have been created, but all map projections will include some distortion. However, different projections allocate the distortion to certain parts of the earth while minimizing it in another, so choosing an appropriate projection for a particular map is important. In GIS, specifying or defining the coordinate system and related information for a set of data is important in producing valid analysis results because inaccurate locations and measurements can diminish the accuracy of calculated values. GIS software usually includes extensive support for a wide variety of standard coordinate systems, and contains tools for conversions and reprojections between systems. See the Specifying Coordinate Systems or Reprojecting Data sections below for more information.

More coordinate system information is available through the built-­in ArcGIS documentation under the heading "Map Projections and Coordinate Systems", as well as in the following articles:

Specifying a Coordinate System

A coordinate system needs to be specified for geographic data so that a GIS can determine how it should be projected. All geographic data displayed on a flat plain will contain some error, so various coordinate systems are used to optimize the spatial manifestation of the data.

Sometimes, imported data will not have a known coordinate system attached. For example, you may download GIS raster data from a public website, but when loaded into GIS software the spatial reference is said to be unknown. The website does not mention which coordinate system was used during data collection. If the coordinate system for a dataset is unknown or incorrect, there are two ways you can assign correct coordinate system.

Your first option is to use the Define Projection tool to specify the correct coordinate system. The Define Projection tool can be accessed by clicking the ArcToolbox button to open the toolbox panel. Then, go to Data Management Tools > Projections and Transformations > Define Projection. You will be able to select the input data, and the new coordinate system desired. You must know the correct coordinate system of the data before using this tool. 

You can also define the projection for data with an unknown coordinate system in ArcCatalog. First, you need to make sure that the data you are going to assign a coordinate system to is not open in ArcMap (the best option is to close ArcMap during this process). Next, navigate to the data (shapefile or feature class) in ArcCatalog, right click to choose Properties, then select the XY Coordinate System tab. Here, you can select a predefined system or import whatever system is being used by another data file. After, you can ensure that the selected coordinate system was applied by adding the data into ArcMap, right-clicking the data layer in the Table of Contents on the left panel, selecting Properties and navigating to the Source tab. Here, in Data Source section, you will see the data is now using the new, correct coordinate system.

If you need to convert data from one coordinate system to another ("reproject" the data), and have a new dataset or feature class with the coordinate system specified, see below for detailed instruction.

Reprojecting Data

Tip: The method described below takes data with known spatial reference and converts it to another coordinate system. To define a coordinate system for data that does not yet have spatial reference, go back to the Specifying a Coordinate System section.

The Project tool in the ArcToolbox is used if data in one coordinate system needs to be converted, or 'reprojected', into another system. For example, you may have data that was taken in latitude/longitude under the WGS 1984 geographic coordinate system, but you would like to convert it into an x,y coordinate projection system, such as a UTM projection.

The Project tool can be accessed by clicking the ArcToolbox button to open the toolbox panel. Then, go to Data Management Tools > Projections and Transformations > Feature > Project if you are projecting a shapefile or feature classes. You will be able to select the input file, an output file, and the new coordinate system desired.

Note: To reproject raster data, you will need to use the Project Raster tool under Data Management Tools > Projections and Transformations > Raster instead. 

Creating Presentation Maps Using ArcGIS 10.x

The Layout View in ArcMap displays map data in a preview layout as it would appear on a page. To switch to Layout View, click the Layout button in the View Toolbar at the lower-left corner of the display area, or select "Layout View" in the View menu. This view allows for arranging multiple frames of data and placing map elements, such as a title, a legend, map scales, and other items. The page format can be changed by accessing the File - Page and Print Setup menu.

In Layout view, map data is presented in a page view within various data frames. By default, one frame (shown in the TOC as "Layers") is already present; choose Insert > Data Frame to add more. For example, if you wanted to publish a figure featuring several maps, one showing South America and another showing the world; each of those maps would be created in a separate data frame section of the TOC. The content, symbology, and labels within each data frame are controlled by adding data, checking and unchecking map layers, and configuring items in the specific section of the TOC. A wide range of frame properties, including background or outline colors, size and position, extent rectangles, and other items can be edited by right-­clicking the data frame and choosing Properties.

Map elements, including a title, neatlines, a legend, a north arrow, and others, can be placed through the Insert menu. Items are easily moved around the layout, and various properties for elements are accessed by right-­clicking and selecting Properties.

For more details, see A quick tour of ArcMapEssential ArcMap vocabulary, and Page Layout from ESRI Online Help or the Publishing Maps tutorial.

Publishing Maps

Export finished map as PDF

When your map is finished, the easiest way to publish the map is to export the map as a PDF file. To do this, go to File > Export Map. Here you can export the map as PDF, or any file type you desire.

Publishing Maps for Distribution with ArcPublisher and ArcReader

Maps created in ArcMap can be exported as Published Map Files (.pmf) using the Publisher Extension to ArcMap, which then allows them to be read by ArcReader, a free map viewer from ESRI. This makes mass distribution or public viewing of GIS maps easy. To obtain ArcReader, users should access ESRI's ArcReader product page.

First, to enable the Publisher extension, go to Customize > Extensions in ArcMap. Make sure Publisher is checked (If it is not available, you will need to run the ArcDesktop setup and select the Custom option to install the extension). Once the extension is enabled, the Publisher toolbar appears. If it does not, go to Customize > Toolbars and check the Publisher toolbar.

The most simple method of publication simply creates a file that directs ArcReader to gather the necessary map data for the published map, but does not package a copy of the data to be transferred along with the file. This method works if the intended audience will be viewing from computers that can access the map data that is referenced in the map file. To publish a simple map file, go to the Publisher Toolbar and select Publisher > Publish Map. Save the file in a chosen location. This saved file is the published map file, and can now be sent to others to view.

Publisher also allows for packaging data with the map, which is necessary if users will not already independently have access to the map data. After creating the published map file, in the above step, click on the Create Data Package button   in the Publisher toolbar. You will be asked to select the .pmf file that was just created. The program will then place additional files in the specified location, which can then be distributed for viewing.

For a more in-­depth example, see the ArcGIS Publisher on ESRI online resource center. 

Adding Point Data From a List of Latitude/Longitude Pairs

Sometimes it will be necessary to convert a list of latitude and longitude pairs into point data. Typically this data will be a table in a csv or Excel file.  To create a point layer from a table:

  • Add the table to ArcMap using the Add Data button or dragging the table from the Catalog Pane to the Table of Contents. 
  • Right click on the table and click Open to inspect the data table.  Check to ensure that the columns containing the latitude and longitude data are in numeric format by right clicking on the column name and clicking "Properties. If the data type of column is not numeric (i.e. String), close the data table and close ArcMap.  Open the table in Excel, change the data type of the column to numeric, then save and close the table.
  • Right click on the table in the Table of Contents and select "Add XY Data."  The Add XY Data window will appear.  Fill out the box with the following information:
    • Choose a table from the map or browse for another table: The name of your table should appear in this box.
    • X Field: The field containing the longitudes
    • Y Field: The field containing the latitudes
    • Description: If this box says "Unknown," click edit and select an appropriate coordinate systems.  It is likely that if you have latitude/longitude pairs, you will choose a geographic coordinate system such as WGS 1984.  If your XY Data is not latitude/longitude pairs, check the documentation or metadata of your table for information on the corresponding coordinate system.

  • Once your entries are complete, click "OK" to add the data to your map. 
  • You may see a warning stating "Table Does Not Have Object-ID Field", the message also indicates what you must do to correct the issue.

After the Event layer is created, add a Basemap or other reference data to ensure that the points appear in the expected location.

Editing Data in ArcMap 10.x

Aside from the ability to view and analyze geographic data, many GIS applications also contain tools that enable data editing. ArcMap contains powerful tools that facilitate editing either graphically on the map, or through tabular or computational editing.

For editing to take place, an editing session needs to be started. By default, editing is turned off when an item is being viewed in ArcMap to protect against accidental changes to the data. However, when updates or revisions need to be made an editing session can be started by turning on the Editor Toolbar (Customize > Toolbars > Editor), then clicking on Editor > Start Editing. If the layers in the Table of Contents are from different folders, you will then select the layer that you want to edit.

Once edits are made, you will need to click on Editor > Stop Editing, which will give you the option to save or discard the changes.

The type and extent of editing you do will depend on how your data needs to be changed. On the Editor Toolbar, there is a list of possible tasks to choose from. The Attributes and Sketch Properties allow viewing and editing of data in tabular form.

A simple example:

Let's say an existing polygon needs to be divided into two sections. First, the target feature--the item you want to edit--needs to be specified--in this case, it will be a polygon. Then, a dividing line will be drawn to bisect the polygon and create two separate features. Use the  Edit Tool   from the Editor Toolbar to select a polygon. The selected feature will be highlighted in blue along it's edges to signify that it has been selected.

Next, select the Cut Polygons Tool  . You will see that the Straight Segment  is automatically selected.

Click a location to start drawing a dividing line through the polygon. To add additional points, click elsewhere on the map. To finish drawing, double-­click on the final point. If the line drawn produces a valid polygon cut, the new section will flash and become a new, separate feature.

 

Tip: A useful component of Editor Mode is the Snapping feature. Snapping can be activated to make the cursor automatically land ("snap") on a nearby point or line when it is within a few pixels. This is helpful when the sketch that you are trying to draw must correspond to certain edges or vertices. To activate Snapping, click on Editor > Snapping > Snapping Toolbar, which opens the snapping toolbar. On the toolbar, you can select which items to snap to (point snapping, end snapping, etc.) by checking those items on and off: 

The Snap to Sketch feature of the toolbar enables you to snap to new sketches that you make while in an active editing mode.

For more about snapping, check out ESRI online help here.

Importing CAD Data Into ArcGIS

ArcGIS can import CAD data in .dwg, .dxf, and .dgn formats. Most importing is done through the ArcToolbox, which can be opened in ArcCatalog or ArcMap using the Toolbox button 

The CAD to Geodatabase tool, under Conversion Tools > To Geodatabase, can import a collection of CAD files and convert them into feature classes for use in ArcGIS.

Tip: To find a tool in the toolbox by name, use the Search button . It can also be accessed from Windows > Search.

To import individual CAD feature classes, the class needs to be projected to the coordinate system that the GIS data is using. To do this, use the Project tool, under Data Management Tools > Projections and Transformations > Feature. The tool will ask you to select the file you want to input, the location to output the converted feature class, and the new coordinate system to use.

If the original feature class is already in correct coordinates, the Feature Class to Feature Class or Feature Class to Geodatabase tools, under Conversion Tools > To Geodatabase, can be used to quickly pull the original classes into ArcGIS. 

More information can also be found in the ArcGIS Desktop help: In ArcCatalog or ArcMap, go to Help > ArcGIS Desktop Help. Select the Search tab, and type in CAD data. Choose Importing CAD data for some helpful info, or explore the other topics.

Converting Map Layers to CAD Format in ArcMap 10.x

Students regularly contact us regarding access to CAD format files. Most of the data we store on the network and much that is available over the web is formatted for the ESRI ArcGIS program. Data sets that you are able to view in ArcMap can also be exported into CAD format. This tutorial will show you how to accomplish this task, and more information on integrating ArcGIS and AutoCAD can be found at ESRI's CAD Integration Resource Center.

Note: Often times CAD data is not in a real world coordinate system. If you would like to match GIS data to existing CAD data, there may be additional steps required once all data layers are in CAD format.

The first step is to find and load the data layers of interest into an ArcMap document (.mxd). Use ArcMap to preview the datasets and to focus the map window on your area of interest. Most CAD applications deal with relatively small spatial areas and therefore limiting the size of the source data files will make storing and transferring those files much simpler. Once you define your area of interest, the second step is to limit the extent of any layers that you intend to convert as follows. 

Reduce Layer Extent

In ArcMap Table of Contents, right-­click on the layer you wish to convert. Select "Data", then "Export Data". 

In the Export Data window, use the down arrow to limit the export to "All Features in View Extent" and specify a location for the output. Click OK. 

When it's done exporting, a subsequent window will ask if you want to add the layer to your map document, select "Yes". After you have reduced the layers you wish to convert into more manageable sizes, use the "Export to CAD" tool to create a CAD format file.

Export Map Layers to CAD Format 

Make sure the ArcToolbox is displayed. If not, click on the red toolbox icon. Browse to the "Conversion Tools", "To CAD" toolbox and open the "Export to CAD" tool (this tool can also be opened by right clicking on the layer -­ Data -­ Export to CAD). 

Select each export layer using the black down arrow to access the layers in your project. As each layer is added, it will appear in the target list. Enter a filename for the output and click OK. 

A status window will open when the process finishes. 

Working with Digital Elevation Models 

This guide contains suggestions for working with DEM files. 

 

Extracting a Digital Elevation Model (DEM) File from a Larger Online Source

A Digital Elevation Model, or DEM, is a raster data typed used to model elevation at local and global scales. Like other types of raster data, elevation values are assigned to cells within a larger grid of values that represent a surface area. DEM's have been created in a variety of resolutions and sizes in order to accommodate various project needs; you can read more about DEM resolution and vertical accuracy differences here.

Downloading area specific data from larger online sources is quite simple.The following tutorial will briefly walk you through the process using the USGS's National Map Viewer. 

1) Navigate to the National Map Viewer here or via your search engine. Below is what you should see. 

2) Next, search for an area of interest to your research or project needs by entering the name of a city, state, or place in the search bar near the top of the screen. For this example, we'll use a local area: Forest Park. 

Alternatively, you can zoom to your location by using your mouse or the zoom controls on the map. 

4) Before the National Map engine can identify what datasets are available for your area of interest, you must specify what type of data you would like to find and download. Use the Dataset menu on the left-hand side of the screen to select the types of data you wish to download. In this case, we'll want Elevation Products (3DEP). 

Dataset subcategories allow you to further parse the data to find exactly what you need. For our purposes (DEM visualization at a local scale), we'll select either 1/3 or 1/9 arc-second DEMs.

5) Once you have selected the types of data you are interested in viewing for your area, you can find available products in one of two ways.

  • If you entered the area of interest into the map search engine, you will notice that the resulting point on the map has a "Find Products" option. By clicking on this, a list of available products for that area is automatically generated and can be viewed on the left hand side of the screen.

  • If you zoomed into the area of interest, make sure that the "Current Extent" radio button is checked near the top of the map. Then, hit "Find Products" on the left-hand side of the screen to view the list of available data sets for your current map extent.

6) From the list of available products for your area, select the items you want to download by adding them to your cart.

7) When finished, select 'View Cart' to review your selected datasets and download the files. 

8) Finally, you can bring the files into ArcMap in order to view them by unzipping the files and saving them in a connected folder. 

Note: When viewing DEM files in ArcMap, it can help to pull in a basemap in order to give context to the region of interest. By changing the transparency of the DEM layer (via the Properties window), you can use actual locations on a reference map to help orient yourself on the DEM.

The resulting transparent DEM, underlain by a basemap, makes it easy to find locations like Forest Park:

 


Creating Contour Lines from a DEM Layer

Creating contours from a DEM layer is very simple and is one of the most common uses of DEM files.

1) Open the Spatial Analyst toolbox and navigate to 'Surface' > 'Contour.'

2) In the tool window that opens, select the input raster (DEM) file that will be used for the contour creation. Specify a location for the output and enter a contour interval. If you want the contours to display in a different metric than the one stored in your raster data (i.e. feet versus meters), fill out the Z factor. For more information on this unit conversion option, see the Tool Help for Contours.

Note: When choosing a contour interval, it's best to visually examine the area being contoured first and make a decision based on the extent and relief of the area. For areas with high relief, it is wise to stay away from picking a small contour interval, as the resulting contours will be very close together on the map and hard to distinguish from one another. For areas with low relief, choosing a smaller contour will add more detail to otherwise uniform topography. Try several different interval levels to see what looks best and depicts the area most accurately! 

3) Hit 'OK' to run the tool. Add the resulting layer to the map in order to examine it. Repeat the process with different contour intervals as needed. Toggling the DEM layer off and on, manipulating the symbology, and adjusting the transparency can assist you in determining whether the contours produced are the best representation of your data. 

4) Given the size of many DEM files, it can be useful to subset your data--extract only the area of interest--in order to reduce the file size and eliminate unnecessary data. In order to do this, zoom into the area of the map that contains the area whose source data you want to extract.

5) Right-click on the DEM layer in the Table of Contents to select 'Data' > 'Export Data'

6) In the dialog window that appears, make sure the 'Extent' option is set to 'Data_Frame (Current).' This will ensure that only the data visible in the current map extent is extracted, rather than the entire raster dataset. 

7) Select a location and name for the resulting image and hit 'OK'. Add the layer to the map when prompted. 

By zooming out, you will see the result of the subset:

8) You can now re-contour this DEM subset as done before! 

For more information on working with contours, check out Desktop Help for ArcMap here.

 


DEM Resources

Below is a list of common sources for DEM data at the national and international level. Local level data is provided for Missouri. 

Resources for National Data:

Resources for International Data:

For Missouri specific data, check out the MSDIS (Missouri Spatial Data Information Service) site here to browse local geospatial data, including DEMs.

Areal Apportioning

Apportioning is the process of dividing and assigning attribute values from one spatial layer to another overlapping layer where the boundaries do not line up to allow simple summing.  Areal apportioning is necessary when researchers want to compile census data for areas that do not coincide with census boundaries such as tracts.  This guide will illustrate how areal apportioning works and demonstrate a simple workflow to accomplish this task in ArcMap using data from the city of St. Louis, Missouri.

 

 

 

 

 

This figure shows the city neighborhood boundaries (black borders) along with the census tract boundaries (gray borders).  These layers do not cleanly line up along their boundaries and this complicates the process of compiling demographic data from the census according to neighborhood.

 

 

 

 

 

 

 

 

 



 

 

 

 

The Central West End neighborhood provides a good illustration of how boundaries do not always overlap cleanly. In this case, the neighborhood includes several complete census tracts in the center but around the edges, there are several tracts that are divided by the boundary. In addition, although the basemap reveals that most boundaries tend to follow streets, the spatial layers were not created by the same agency and even when following the same streets, there can be misalignments. 

 

 

 

 

 

Assigning numeric attributes to the neighborhoods from mismatched geometry such as the census tracts requires some apportioning of values and this is usually accomplished based on the area of the tract that falls within the boundary of the encompassing neighborhood.  If the tract falls completely within the neighborhood, 100% of the value is assigned, if only half of the tract falls within the neighborhood, only 50% of the value is assigned.  The other 50% of the value would be assigned to the adjacent neighborhood.  This operation is accomplished in ArcGIS Desktop using the following workflow:

  1. The source layer for the attributes must be converted to a "Feature Layer" which is a temporary layer in the map document that enables the apportioning to occur automatically (see this ESRI documentation for details).

    • Open the Make Feature Layer (MFL) tool
    • Specify your source shapefile or feature class as the Input
    • Set any attributes that need to be apportioned to "Use Ratio Policy"
    • Run the tool...a new layer will be added into your map Table of Contents


       
  2. Apportioning occurs when you run an overlay tool such as Intersect.
    • Open the Intersect tool
    • Add the layer to be populated
    • Add the source layer for the attributes (from the MFL tool)
    • Set the output location and name
    • Run the tool
      • If a selection exists on one of the layer, only those features that are selected will participate in the operation and appear in the results.
    • Intersect creates a new layer that includes all boundaries from the input features and areas that overlap contain any visible attributes from all of the input layers.

 

The results in this case only included the Central West End (CWE) neighborhood.  Examining the attribute table finds that values for the POP10, WHITE10, and BLACK10 attributes have been apportioned into each tract according to the area within the CWE boundary.  The data type for these values are 'float' since they are the result of a calculation.

 

To process all of the features in a layer, run the tool without any features selected.  The result can be simplified further by hiding (turning off) any fields in the input layers that are not required in the output.  To compile results based on one of the original input geometries, use the Dissolve tool to combine the intersected features using a field that uniquely identifies the areas you want to combine...in this example that would be the neighborhoods.

 

Resources

ESRI Documentation:

GIS Stackexchange: 

 

Last updated 4/16/2020

There are several tools in ArcMap to calculate distance between features. These can be found under the Proximity toolset:

Near: Near calculates distance and information on the nearest feature between input and target features. 

 
Generate Near Table: Generate Near table does the same thing as Near, however no changes are made to the input layer and the output is a table. 

 

Summary of Near operations. Source: ESRI

 

Point Distance: Calculates distance between two sets of points within a search radius. 

Summary of Point Distance operation. Source: ESRI.

 

 For these  tutorials, we will use these data:

  • Libraries_STL_Project.shp: Points shapefile of library locations in St. Louis City. 
  • Schools_STL_Project.shp: Points shapefile of school locations in St. Louis City. 
  • BikeFacilities_STL_Project.shp: Polyline shapefile of bike paths in St. Louis City. 
  • STLcity_Project.shp St. Louis City boundary shapefile. 

All of these shapefiles can be found in GISPUBLIC. These shapefiles were formatted (projected to appropriate projection, clipping features based on city boundary) for these tutorials. 

Near Tool

Using the Near tool, we will find the distance between libraries(Libraries_STL_Project.shp) and bike paths (BikeFacilities_STL_Project) in the City of St. Louis.

  1. Click on the Search button in the ArcMap toolbar. A Search window should appear on the right-hand side of the workspace. 
  2. Type Near in the search box and select Near(Analysis). 
  3. In Input Features, select Libraries_STL_Project. In Near Features, select BikeFacilities_STL_Project. Click OK. |
  4. Right-click on Libraries_STL_Project and scroll towards the end of the attribute table.
  5. You will see NEAR_FID, which is the feature ID of the nearest bike path from the specific library and NEAR_DIST, which is the distance to the nearest bike path in feet. 

Generate Near Table Tool

Using the Generate Near Table tool, we are going to generate a near table based on the distance of schools in St. Louis (Schools_STL_Project.shp) from the nearest bike path(BikeFacilities_STL_Project.shp) .

  1. Click on the Click on the Search button in the ArcMap toolbar. A Search window should appear on the right-hand side of the workspace. 
  2. Type Generate Near Table in the search box and select Generate Near Table (Analysis). 
  3. Let’s determine how far schools are from the nearest bike path. For Input Features, select Schools_STL_Project and select BikeFacilities_STL_Project for Near Features. Choose a location to save the Output Table by clicking on the button on the right-hand side under Output Table. 
  4. Uncheck Find only closest feature and keep everything else the same. This way, you will get the distances from various near features. Click OK. 
  5. The near table should appear in your Table of Contents. Right-click on the table and click Open. 
  6. You will see a table with these fields: 
  1. OBJECTID: Record locator for each row. 

  1. IN_FID: The feature ID of the input features, which in this case, is Schools_STL_Project. You can find what school the FID of these features refers to in the Schools_STL_Project shapefile. 

  1. NEAR_FID: The feature ID of the near features, which in this case, is BikeFacilities_STL_ProjectYou can find what bike path the FID of these features refers to in the BikeFacilities_STL_Project shapefile. 

  1. NEAR_DIST: The distance between a specific input feature and near feature. In this case, it would be the distance between a given school and bike path. Since the data was projected in feet, the distance is given in feet. 

  2. NEAR_RANK: The rank of the near feature(bike path) is given on how close it is to the input features (schools) in comparison to the other near features.

Point Distance 

Using the Point Distance tool, we will find the distance between schools(Schools_STL_Project) to libraries(Libraries_STL_Project) in St. Louis City. 

  1. Click on the Click on the Search button in the ArcMap toolbar. A Search window should appear on the right-hand side of the workspace. 
  2. Type Point Distance in the search box and select Point Distance(Analysis). 
  3. For Input Features, select Schools_STL_Project and for Near Features, select Libraries_STL_Project. 
  4. Choose a location to save the Output Table. Choose a location to save the Output Table by clicking on the button on the right-hand side under Output Table. 
  5. Leave the Search Radius (optional) blank and click OKA output table will appear in the Table of Contents. 
  6. Right-click on the output table and click Open. You will see a table with these fields: 
  1. OBJECTID: Record locator for each row. 

  1. INPUT_FID: The feature ID of the input features, which in this case, is Schools_STL_Project. You can find what school the FID of these features refers to in the Schools_STL_Project shapefile. 

  1. NEAR_ID: The feature ID of the near features, which in this case, is Libraries_STL_ProjectYou can find what bike path the FID of these features refers to in the Libraries_STL_Project shapefile 

  1. DISTANCE: Distance between each input and near feature. In this case, the distance is in feet.