An introduction to mapping as a CAR tool

Offentliggjort 07/30/2008

Af Jennifer Lafleur

- Gilbert Grosvenor, Editor, National Geographic, 1903-1954

Although mapping can be used to visually enhance any story, in some cases it’s the key to the story. Geographic Information Systems (GIS) allow you to map one or more sets of raw data, which can show intersections between data sets or clusters in one data set that you would not be able to find otherwise.

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 you’re dealing with county names and you 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 it 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.

Before El Nino hit California, the San Jose Mercury News wanted to look for potential mudslide problems in the Santa Cruz Mountains. The story we did addressed the fact that many new building permits have been issued in areas susceptible to landslides and debris flows by overlaying permit data and geological data on one map.
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, which is compatible with ArcView, the mapping software we use at the Mercury News.

The 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! which 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. The technique is not perfect. You'll never get a perfect match of every address. But once you've run the process once, you can go back to the addresses that didn't match and do a pretty good estimate of where they are.

Being able to join the two sets of data -- the landslides and the permits -- allowed us to see where clusters of building permits occurred on or near areas where potential landslides were. From that point, we could go out and talk to experts and real people about our findings.

In 1992, Steve Doig, then of the Miami Herald overlaid wind speeds and building damage after Hurricane Andrew hit Florida. The mapped showed something that no other tool would have revealed: an area with minimal wind speed, yet some of the worst damage.

“I've always conceptualized CAR as ‘finding the patterns’ in the data,” Doig said. “And spatial patterns are perhaps the easiest to understand. I first got a GIS package in order to work with 1990 census data, and I saw how much easier it was for reporters to see the story in the data when I could give it to them mapped. Not only does mapping make good end graphics to go with a story, but perhaps even more important it helps sell a story to editors and reporters.”

The Mercury News has used maps to show precinct-by-precinct voting results against other data. For example, when a major transportation ballot measure was passed, we mapped results against where major traffic routes were. Votes were strongest where people with the worst commutes lived.

A few years ago, Ron Campbell of the Orange County Register mapped bank locations against demographics. The map showed a pattern that would have been obvious in no other formation than a map. “In everywhere but Santa Ana, you could practically stub your foot on a bank there,” Campbell said. Campbell purchased a database of bank locations and mapped it. “That made it clear,” he said. “There was a donut in Orange County with a hole in the center without banks.” From there he started looking at demographics.

The Orange County Register also has used maps to display voting by census tract. “You have to develop precinct votes to census tracts,” Campbell said. “But when you get over the conversion problem, you can display how votes differ from place to place.”

“I think the real value to mapping is in the cliché ‘a picture being worth a thousand words.’ You can go on and on about the trends but when you put the data on a page in color people can tell what’s going on,” Campbell said.

When you’re trying to show clustering of data geographically or looking at trends between to geographically based data sets, consider mapping it. Some of the most commonly used GIS programs are Atlas GIS, Mapinfo and Arcview. It’s probably worth talking with some of your local planners to find out what software they use to find something compatible.

“In just about any case when I’m dealing with a large set of data, if I can map it I will. Numbers represented visually let you see nuances that your eyes never pick up in a data grid, even for the simplest data set,” Napolitano said. “Mapping is one of the most powerful tools available to reporters.”

Once you select your software, join your local users group. Most of the mapping folks from local government participate in those groups and it’s a great way to do some nerd-bonding and find resources for maps. For a list of local ArcView users groups, go to www.esri.com.

Here are some other ideas of data to map in your area. Anything that would be more meaningful shown geographically has potential:

• City Services -- streets that get cleaned more than others, police patrolling
• Crime
• Flood zones
• Pollution
• Home prices
• Election results versus factors form the election (transportation measures against where worst commutes are)
• Traffic patterns

Mapping Resources

• CrimeMap: sponsored by the National Institute of Justice's Crime Mapping Research www.ojp.usdoj.gov/cmrc/faq/welcome.html, they also have a listserv Center.
• U.S. Geological Survey: mapping.usgs.gov
• Association of American Geographers: www.aag.org/
• The Consortium for International Earth Science Information Network (CIESIN) wwgateway.ciesin.org
• The Geographer's Craft at the University of Texas: www.utexas.edu/depts/grg/gcraft/contents.html
• Naitonal Center for Geographic Information and Analysis: www.ncgia.ucsb.edu/ncgia.html

For more information, check out some of these books:

• Visual Display of Quantitative Information, By Edward Tufte, 1992
• Elementary Statistics for Geographers, by Gerald Barder and James E. Burt, Gerald M. Barber, 1996
• How to Lie With Maps, by Mark Monmonier and H. J. De Blij, 1996
• Computer-Assisted Cartography: Principles and Prospects, by Mark S. Monmonier, 1982

Some of this material by Jennifer LaFleur was previously published in Uplink

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• Computerstøttet journalistik
• GIS og kortanalyse