Geocoding is the process of converting a textual representation of place into spatial coordinates. If you think of your home address, it consists of a house number, street name, city, state, and zip code. Each of these pieces are important for the delivery of goods and services; or for the arrival of new friends to your door. We simply type the information into our phone or GPS and are presented with turn-by-turn directions to arrive at our destination. This process is routine and appears simplistic but relies on a series of spatial operations that start with geocoding. Our familiar addresses are not immediately translatable into a unique point when we want to represent locations on a map or use some network analysis to determine a route. Geocoding performs that translation and allows us to convert single addresses or even long lists of them (batch geocoding) into points in a spatial dataset that are useful for mapping or determining distance or travel time.
Geocoding requires a list of one or more addresses and an “address locator” that will convert that information into point locations. Address locators operate at levels of complexity ranging from a simple lookup table to a more complex analysis that interpolates the location of a house number along a linear street segment. Lookup tables are lists of address information with an associated set of coordinates representing the point to which the address refers. These lists can link Zip Codes to the centroid of that area or link full addresses to a point location based on the position along the roadway or the centroid of an actual property parcel of building footprint. Interpolation involves using linear street features that also contain attributes storing the starting and ending house numbers; the locator finds the correct street feature and then estimates the location of the target address number along the segment assuming even distribution of values. The level of detail (accuracy) available in an address locator is directly related to the cost of creating such a resource. Some locators apply a cascading model whereby the most accurate match is sought but if that is not successful, matches at decreasing levels of detail (i.e. zip code, city, etc.) are attempted until a match is obtained.
There are several resources available to the Washington University community for geocoding. See the below links (also in the sidebar) for more information. The Address Locators page provides descriptions and access instructions. The Geocoding Workflows page presents step-by-step instructions for performing geocoding in several different software tools. For further details on geocoding in general and on specific tools, see the Documentation and Training page.
Please contact Zachary Szczepaniak or Data Services if you have any questions.
