MAR Geocoder User Guide. Geocoding is the process of assigning a location in the form of geographic coordinates (often expressed as latitude and longitude) to geographic data. This is done by comparing the descriptive geographic data to known geographic locations such as addresses, blocks, intersections or place names. For example, 2500 Q ST N.W. is geocoded to the actual address of 2500 Q STREET NW and assigned the X,Y coordinates of 395476.16, 138058.36.