Cartographica has a powerful file-based Geocoding capability, but to use it, you must gather data first from some compatible source (such as the US Census Bureau). 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. We are expecting to incorporate direct access to online geocoders in a future release of Cartographica, but for now, all geocoding must be done with TIGER files.
Since 2007, the data provided by the Census Bureau comes in more convenient shape files. If you need to geocode with older data (sometimes necessary when trying to match old addresses on roads that have been realigned, moved, or destroyed) then follow the instructions in our previous article on Geocoding with TIGER/Line files.
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.
- Locate your TIGER/LINE Shapefiles on the server by selecting the State and County that you are interested in using for geocoding.
- Once you've selected the county, you can download one of a number of files. The one that you need is the "All Lines" file for the county. If you click directly on the text for "All Lines" it should download, otherwise, you'll need to check the box next to it and click on the "Download Selected Files" button.
- After the files are downloaded and unzipped, import the .shp file (use Import Vector Data... from the File menu, or drop the files into your map) into your document.
- 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), and the Street Name. As of version 1.1 of Cartographica, the Street Type (Rd, Ave, etc.) is presumed to be included in the Street Name if you don not select a Street Type column. 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. If you do this, the text is compared against the state field in the addresses being geocoded, but is not mapped to the Tiger file.