EVERY work day, police officer Michael Byers takes eight colored pencils and draws on a map of Durham, N.C.He is tracking major crimes. If the procedure seems a little archaic ("something right out of caveman," Officer Byers laughs), the idea makes sense. Each crime has its color. By pinpointing when and where the crimes occurred, officer Byers hopes to spot patterns and trends. Add the power of a computer (as Durham soon will) and the process becomes a geographic information system or GIS. Mike Watson, chief appraiser of the Bell County (Texas) Tax Appraisal District, knows what GIS can do. For years, his office used big paper maps to track property ownership and value. When the county installed a GIS system a few years ago, he and his colleagues were surprised to discover land they never knew existed before. Some plots had been overlooked and gone untaxed for years. Meanwhile, the appraisers found that other plots fully described and collecting delinquent taxes didn't exist at all. GIS is a simple idea. "You have used GIS all your life," says Richard Pabst, manager of GIS solutions for IBM's Mid-Atlantic area. For example, some-one wanting a tennis racket might look up sporting goods in the Yellow Pages, find a store's address, then use a map to find how to get there. That's GIS, Mr. Pabst says. "You took some information and an objective and tied them to together." A computer usually does this by digitizing a paper map or aerial photo (turning it into a series of dots, lines, and spaces that the computer can display). Each dot, line, or space is linked to pieces of information stored in the computer. So, a dot might represent the number of people living at that coordinate, their age, or their income. A line on a road map might be tied to data identifying it as a paved road, a superhighway, or Interstate I-70. A paper map might show some of these details. GIS allows people to play with all the variables and ask sophisticated questions. For example: Show all the places in California where most of the residents are at least 50 years old, earn between $35,000 and $50,000, and have bought a car in the last 18 months. GIS computer systems have been around for more than 20 years. In the early '70s, utilities began using the technology to track maintenance and react to problems on its power lines. Those early systems required expensive mainframe computers and software. As hardware and software costs have come down, more businesses are looking at GIS for all sorts of uses. In a large room of an IBM facility here in Raleigh, N.C., company officials show how one of their IBM PS/2 desktop machines might handle a retail store marketing decision. The screen displays the location of a store and all its competitors in the area. The retailers wonder whether they should move to a new location. So GIS overlays another map on the display, breaking up the city by census tract. The map displays the store's survey data, which shows that most of the store's customers come from right in the neighborhood. Probable conclusion: Don't move. The possible uses are endless. A real estate agent could pinpoint in a few minutes all the listings for, say, a two-story house within five minutes of a school, the library, and the post office. Officer Byers in Durham could analyze all the grocery store holdups between midnight and 4 a.m. A 911 emergency center could tell firemen not only the address of the fire but the quickest way to get there. Bell County, Texas, is instituting such a system. State political parties and independent groups are using GIS to propose changes in United States congressional districts. Eventually, GIS will probably serve as a linchpin for other technologies. INDEED, there are so many possible uses that early users have been frustrated by the technological barriers. For one thing, GIS requires a great deal of computer power. When Brevard County, Fla., started installing IBM's GIS system three years ago, it had high hopes of running it on its IBM mainframe. That way everyone in the county from police to tax appraisers could tie into one centralized mapping system. The plan didn't work, however, because the mainframe couldn't handle the county's regular work along with the GIS. At the moment, the system needs three to four hours to draw an intricate map and another two to accept a change. That's too long, says Michael Wentworth, the county's director of geographic research. A tax appraiser would need a whole day just to add a subdivision on the county map. "I'm still a believer in GIS," says Mr. Wentworth. But "they sold the software without the technology really being there." Then there's the question of expertise. "Getting a map out is easy" with GIS, says Daniel Olasin, president of Intelligent Charting Inc. "Getting the right map out - that's where the challenge comes." Mr. Olasin's company provides that expertise, taking an organization's data and making maps that help people reach a decision. The drawback with that approach, he says, is that companies can't play around with the data and conjure up scenarios on their own. Often, that turns out to be unimportant to businesspeople, Olasin says. "They think that they will play 'what if?' but they don't do it." But for those companies that do need to play "what if?" Intelligent Charting is working on hooking up its customers with its mainframe computers, so they can have almost immediate access to newly drawn maps. Nearly everyone agrees that GIS will take off as a technology. Eventually. "It's so exciting, it's frustrating," says Mr. Watson.