Although mapping can be used to visually enhance any story, in some cases it's the key to the story. Geographic Information Systems (GIS) allows you to map one or more sets of raw data, which can show intersections between data sets or clusters in one data set that otherwise you would not be able to find.
Most of you have used a database manager to look at data in many ways. With geographically based information, that's easy to do - if for example you're dealing with county names and know where those counties are. But what if your data is listed by Census tract? You probably wouldn't look at a list of tract numbers and say: "Hey, look there at tracts 5001.02 and 5002.03. Isn't that interesting." Seeing the same information on a map makes the data much more powerful.
When Carol Napolitano of the Omaha World-Herald needed to look at trends in more than 300,000 crime incidents for the last seven years, she used a map. "The fastest way to see is visually," Napolitano said.
Flowing foundations
Before El Nino hit California, the San Jose Mercury News wanted to look for potential mudslide problems in the Santa Cruz Mountains. By overlaying permit data and geological data on one map, our story addressed the fact that many new building permits have been issued in areas susceptible to landslides and debris flows.
Getting the maps of the slides and flows was easy (well, sort of). We were lucky in that the U.S. Geological Survey uses ArcInfo mainframe software to do its mapping. ArcInfo is compatible with ArcView, the mapping software the San Jose Mercury News uses.
The San Jose Mercury News also obtained a database of building permits since 1985 from the Santa Cruz County planning department. We would have loved to have gone back to 1982, but the county started computerizing its records in 1985. The building permit data contained addresses for all the building permits.
Using a technique called "geocoding" (as opposed to "Gee, coding!" that programmers say when they get really excited about something they've done), mapping software converts addresses to latitudes and longitudes and, eventually, to points on a map.
Jennifer LaFleur of the San Jose Mercury News describes overlaying building permit data with geological mudslide data to predict potential trouble areas and talks to other mapping practitioners.