Map Hints
This chapter is about maps, and how they relate to GPS use. We'll look at topography, the compass, mapping, scale, projections, UTM, datum, and the U.S. Geological Survey.

The sections on UTM and datum are especially important when using a GPS receiver with a map.


Topographic maps show the physical features of the land, usually including "contour lines" of constant elevation.

Contours take some getting used to, but once you learn "how to look at them", they add a third dimension to a flat map. Mountains, plains, ridges and valleys appear, and they usually match what you see out there. Smaller features can fall between the contour lines.

One easy source of confusion is which direction is "up", but there is usually a peak, river, or lake nearby to cue off of. Elevations are given for major contour lines. When there are no landmarks, the contour of the land is usually easy to read and follow.

Color Frills


To be useful, maps should be small enough to use, but show good detail.

A map covering a large area like the U.S. or World will have a small scale (1:10,000,000).

A map covering a small area like a county or town will have a larger scale (1:24,000).

Large scale means the size of everything on the map is larger - closer to actual size. There are more scale examples in the USGS section.

Sea Anemone



Maps are a flat rendering of the surface of the nearly-spherical Earth. Projection makes flat maps useful and gives them accuracy, but there are always compromises. Maps of the world appear in different projections to serve different purposes.

On a Mercator (cylindrical) projection, scale and distances vary widely, but shape and angles are locally true. Finding your location is easy because the meridians (longitude) and parallels (latitude) are usually straight lines.

Various Lambert (conic) projections are more uniform in scale, but parallels and meridians can be curved.

On large-scale maps (of smaller areas) projection is less important. Shape, scale, and distance should be reasonably uniform.

NEXT: Coordinates, UTM, Map Prep, Datum

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