The Mapping Specialist

Vol VIII, No. 2 - Fall/Winter 2000

Contents | In Focus | Mapmaking | Geonews | Profile | Quiz

MAPMAKING
Cartographic Fact or Fiction

One of the most challenging aspects of cartography is the search for "geographic truth." In other words, where do we find the most authoritative information to show on our maps? The search for this "truth" is much more complex than one would think.

Many people assume that cartography is an exact science.  If it's on a map, it must be right.  We have found that our real challenge is determining whether a source is correct so the map we create is accurate.  Even map sources one would assume to be error-free could be outdated and therefore unreliable.

MSL's first step in producing a street map is to obtain the most recent commercial maps published to compare coverage, content, and design.  Next we contact every city, village, and town (township) in the area to be mapped to procure the latest edition of the municipality's official planning or street map.  While the research material is in transit, our cartographers build the street and boundary linework from the most current digital map data.  These data -- obtained from the U.S. Geological Survey or Census Bureau -- are scaled, cleaned up, names added, and design specifications applied.  In general, extant digital data are incomplete and out-of-date.  After the official maps are obtained, additional detail is added to the digital compilation.

Recently MSL undertook a project to build a street-level map of Dane County, our home.  Our goal was to produce a map of unquestionable quality and accuracy.  But mapping the area we see every day proved to be quite challenging.  Many municipalities produce excellent, up-to-date maps that can be used as a reference.  However, even on the best municipal maps, one can find misspellings, inconsistencies, and outright errors.  We also find discrepancies in spellings -- is the name two words, is the correct street labeled, is it spelled right?

Some municipalities lack up-to-date and accurate maps.  In trying to obtain sources from municipalities, we have been told the following:

"Yes, our map is up-to-date.  It was re-done in 1984."

"Yes, we have a map, but it's on the wall; you can come [to New Hampshire] to look at it, if you want."

"We just use the map in the phone book if we need one."

"Our newest map is from 1972."

In fact, one map from a Pennsylvania community proclaimed: "This drawing is not to scale and may not be accurate.  It is provided for convenience only and may not be relied upon for any purpose." Obviously this poses a problem.

Our solution for the Dane County project was to field check every corner of the county to verify each name and also to apply new subdivisions, which are not noted on the planning maps.  This took time and, of course, money.

Dane County is roughly 1,202 square miles.  More than 4,700 miles were logged during the field check over a five-week period.  Two staff members drove the streets, one verifying data and the other watching the road.  Other staff contributed by verifying the streets in their community.  As a result of our efforts we found that if we accepted the "official" map verbatim, our map would not be as accurate.  However, the additional time and associated costs of salary, mileage, and correcting the map are things a client needs to weigh when estimating costs.

In the end, when the cartographer and the editor sit down to determine the accuracy of our final product, what faces them are divergent sources, of which no two agree.  How do we determine which source is right? Is the "official" municipal map better than the chamber of commerce map? Is the state DOT more authoritative than the local municipality? These are some of the "road blocks" facing us in our quest to provide you with the geographic truth!

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