From version 1.2 forward of Cartographica, we support using the Bing Geocoding service, which is an excellent alternative for bulk and non-US geocoding. This article describes using the built-in geocoder which is designed to work with data sets that meet certain criteria. This particular article deals with using US Census Bureau TIGER files with the internal geocoder.
Most data is accurate to the last census update and may be more recent, based on the government's move to modernize and increase accuracy in the data. Keep in mind that if you are trying to geocode an old address, your accuracy may suffer if the data is too new, since some street realignments, renamings, renumberings, and removals may have changed the landscape since the address data was taken.
First, you need to figure out the area of your search. Generally speaking, you want to limit geocoding to a limited number of counties, to reduce the amount of work necessary on your computer. However, if you must do a large area, or if your area is undefined, there are geocoding services that can do bulk geocoding for a small fee.
Here are the step-by-step instructions:
- Locate the TIGER files on the Census Bureau web site. First, go to the TIGER home page, then select the particular year you're interested in. As of this writing, the TIGER 2007 files are the most recent, and they are in shape file format. Unfortunately, as of this writing, they do not contain the address fields and thus cannot be used for geocoding. Future versions of Cartographica will also import the address map files necessary to link these files up as the previous versions of the TIGER databases did.
- Locate your TIGER/LINE 2006 files on the server and download the county(ies) that you are interested in using for geocoding. After unzipping the files, select Import Vector Data... from the File menu and then select the .RT1 file for import. This will import all of the TIGER data for that county. Be patient, it can take a little while.
- Once the file(s) are loaded, you may remove any additional layers unless you need that data for another purpose. The only important layer for geocoding should have "(Complete Chain)" in it's name. Once you've prepared the file with the geocoding layers, you may want to save the Map file from Cartographica so that you can use it for geocoding that area in the future, without having to go through the download and import process.
- If you need to geocode more than one census area, you need to choose whether to merge the two layers into a single layer and use the new layer as the geocoding layer, or to run the geocoder twice, once with each layer selected.
- The next step is to configure the geocoder. Choose Geocoder Options... from the Tools menu. If you are using standard TIGER/Line files, Cartographica should set up the geocoder by default to use a layer that looks like an imported TIGER/Line file. In most cases, not only is the layer determined, but the field names are chosen as well. If you are using a file from a different source, or of a different vintage, you may need to set up the individual field names. At a minimum, Cartographica requires: Numbers From and Numbers To (for either side of the street or both), the Street Name, and Street Type (Rd, Ave, etc). Each of the other entries (prefix and suffix, zip codes, state, and city) are optional but will increase the accuracy. In the case of State, you may type in value to match the State section of the address.