Introduction to Topographic Maps Banner link to home page GeoSTAC Link to Department of Geosciences at Idaho State University
by Jim Riesterer . . . . . . . . . . Edited by Scott Hughes, Dan Narsavage & Diana Boyack

Topographic Maps Tutorial

Introduction & Materials
What is a Map?
Using Topo Maps
Map Scale
Reference Datum
Map Projections
Grid Systems
State Plane
Public Land Survey
Vertical Scale
Creating Profiles
Vertical Exaggeration
Calculating Slope
Using a Compass
Magnetic Declination
Get a Bearing
Go from A to B
Find Self on a Map

Topographic Maps Field Exercises

Exercise 1
Exercise 2
Exercise 3
Exercise 4

GeoSTAC Home

Field Exercises
April 7, 2008

What is a Topographic Map?

What is a Map?

A map is a way of representing on a two-dimensional surface, (a paper, a computer monitor, etc.) any real-world location or object. Many maps only deal with the two-dimensional location of an object without taking into account its elevation. Topographic maps on the other hand do deal with the third dimension by using contour lines to show elevation change on the surface of the earth, (or below the surface of the ocean).

Compass Image

The concept of a topographic map is, on the surface, fairly simple. Contour lines placed on the map represent lines of equal elevation above (or below) a reference datum. To visualize what a contour line represents, picture a mountain (or any other topographic feature) and imagine slicing through it with a perfectly flat, horizontal piece of glass. The intersection of the mountain with the glass is a line of constant elevation on the surface of the mountain and could be put on a map as a contour line for the elevation of the slice above a reference datum.

Parts of a topographic map

The title of the quadrangle is printed in the upper and lower right corners of the map. In addition to the title of the quadrangle itself, the titles of adjacent quadrangles are printed around the edges and at the corners of the map. This allows you to easily find a neighboring map if you are interested in an area not shown on your map. In addition there is information about the projection and grid(s) used, scale, contour intervals, magnetic and declination.

The legend and margins of topographic quadrangles contain a myriad of other useful information. Township and range designations, UTM coordinates, and minute and second subdivisions are printed along the margins of the map. *Section numbers (from the PLS system) appear as large numbers within a grid of lines spaced one mile apart. The legend also contains a road classification chart showing different types of roads (paved, gravel, dirt, etc.).

Perhaps one of the most important sources of information on a topographic map is the date of revision, printed to the left of the scale. Although large scale topographic features (such as mountains) take millions of years to be formed and eroded, smaller scale features change on a much more rapid scale.

The course of a river channel may change fairly rapidly as a result of flooding, landslides may alter topography significantly, roads are added or go out of use, etc. Because of these changes, it is important to have a fairly recent (or recently updated) topographic map to ensure accuracy. On most topographic maps, the date of the initial publication will be shown, along with the most recent revision of the map.

There are many features (buildings, swamps, mines, etc.) that are designated on topographic maps, which are not described in the map legend. Refer to the USGS Booklet on topographic map symbols to learn more..

Continue to ... Reference Datum ...

The U.S. Geological Survey publishes many helpful booklets that are now available on the web. Below are a few links to helpful sites regarding these products.