Geology 101 - Introduction to Physical Geology
Photos of Pacific Coast, Cascades, Columbia Plateau
Wenatchee Valley College logo
Lab - Topographic Maps

Introduction

Topography is the shape of a surface, in this case the surface of the earth. When you read a topographic map, you are reading the shape of the earth's surface covered by the map area. Reading topographic maps is an important skill for geologists and anyone who needs to see, from a broad perspective, the shape of landforms and how different landforms relate to each other.

The topography of the earth tells us something geological. Geologic processes such as mountain-building, volcanism, streams, erosion, along with the added effects of human activities, shape the earth's surface. Whether the landform is a flat plain or a hilly area, whether it has steep mountains with jagged ridges, or whether it has ridges and valleys that run parallel to each other or radiate in all in directions, they all relate to the geologic processes that have occurred there.

Topographic maps reveal aspects of earth's surface, its hills and valleys, lakes and streams, towns and roads. Geologic maps show information not depicted on topographic maps, including where the mappable bedrock units occur on the map area, the places where bedrock units are covered by thick deposits of mappable sediment units, and the geologic structures that are exposed at earth's surface and continue to some depth inside the earth's crust.

It is common practice for a geologic map to be combined with a topographic map. A geologist will usually start working with a topographic map as the base for constructing a geologic map. He or she will mark on the topographic map the location of different rock types, the contacts between the rock types, and structural data such as strikes and dips of beds and faults.

The most common way of representing three-dimensional topography on a two-dimensional map is through the use of contour lines. A contour line is a continuous line of the same elevation. Learning how to read topographic maps is an exercise in learning how to read contour lines. With practice, you can look at a topographic map and, through its contour lines, visualize the landscape.

Advance Preparation and Materials Needed

Materials Needed

Geology Learning Outcomes

By performing and completing this lab, you will be able to use a topographic map to read the shape of the land, find point elevations, find and specify locations, measure distances, state and use the map scale, specify the compass directions and magnetic declination, find the contour interval, tell which way is uphill and which way is down from any given point, tell which way streams and rivers are flowing, distinguish ridges from valleys, distinguish steep slopes from flatter areas, draw a topographic profile, and measure and calculate gradients.

This will improve your ability to do achieve the following course outcomes:

Methods

To complete this lab, you will conduct the following types of observations, measurements or calculations

Lab Procedures

There are three parts to this lab: developing your topographic map reading skills by working with simplified diagrams that illustrate key elements of topographic maps; practicing your map-reading skills with snippets from real topographic maps; and applying your skills by interpreting an actual quadrangle topographic map.

Refer to the Lab Assignments Grading Rubric for a reminder of what constitutes a well-performed lab.

Part I. Reading contour lines and elevations, distinguishing slopes, and applying the rule of Vs

In this portion of the lab you will work with simplified diagrams that will build your skills at reading key elements of topographic maps. Consider the questions posed below each diagram. They will help prepare you for completing the lab worksheet. Refer to the Rules of Contour Lines maps on the maps Basics page.

Topographic map diagram 1

Schematic diagram with two topographic small map snippets of the same size, with the same scale and contour interval.
There are nine contour lines in the map on the left and there are two contour lines in the map on the right.
Click on the map to open a larger version in a new window

Topographic map diagram 2

Schematic diagram of a topographic map with contours showing a hill.
Click on the map to open a larger version in a new window

The topographic map above shows a hill with a peak elevation of 2574 feet above sea level. Four valleys and four ridges radiate from the peak.

Topographic map diagram 3

Schematic diagram of a topographic map with two streams and contours to be labeled.
Click on the map to open a larger version in a new window

Topographic map diagram 4

Schematic diagram of a topographic map with two streams and contours to be labeled.
Click on the map to open a larger version in a new window

Part II. Map Snippets

This portion of the lab, including the images copied from US Geological Survey maps, was originally created by Tom Braziunas. It is modified and used with permission. You can click on the images to view them in a separate browser window.

Carkeek Park

detail from topographic map of Carkeek Park in Seattle, WA

Above is a small portion of a topographic map showing a road and a creek (blue-green line) in Carkeek Park, Seattle. We assume north is toward the top, as nothing indicates otherwise.

detail from topographic map of Carkeek Park in Seattle, WA

More of Carkeek Park is displayed on the portion of topographic map shown above. Note that every fourth contour line is heavier and labeled with heights in feet. These heavier lines are "index contours". The difference in elevation between adjacent contour lines (all contour lines including the lighter ones) is called the "contour interval".


Green Lake

detail from topographic map of Green Lake in Seattle, WA

The contour interval on this map is 25 feet.


Blake Island

detall from topographic map of Blake Island in Puget Sound

The map above shows Blake Island in Puget Sound, a few miles west of Seattle. The contour interval of the map is 25 feet and the index contours are every 100 feet. The numbers "25" and "36" refer to square mile sections that are part the Public Land Survey System.

By now, you have learned how to determine for yourself that the highest point on Blake Island is between 250 and 275 feet in elevation above sea level.


Grand Canyon

detail from topographic map of the Grand Canyon

This topographic map shows Isis Temple, a butte in the Grand Canyon, Arizona which is 7012 feet above sea level at its peak. Look closely and you will see that the contour lines are closer at some elevations (the steep cliffs) and more broadly spaced at other elevations (the gentler slopes).


Florida

detail from topographic map of Florida

This map shows a sinkhole region in Florida. Note that hachure marks mean that the contour lines drop in elevation instead of rise. Some of these sinkholes are deep enough to be filled with water and contain lakes.


Part III. Complete Quadrangle Topographic Map

In this part of the laboratory on topographic maps, you will use an actual topographic quadrangle map published by the United States Geological Survey. A quadrangle is a specific part of the earth's surface bounded by designated lines of latitude on its northern and southern boundaries and by designated lines of longitude on its eastern and western boundaries. Refer to the Map Quadrangles, Latitudes, and Longitudes section of the maps Basics page for more information.

To be ready to begin working with a complete, published topographic map, here are some questions that you should be able to answer in advance:

« Back to TOP


Geology 101 - Introduction to Physical Geology
Lab--Topographic Maps
Created by Ralph L. Dawes, Ph.D. and Cheryl D. Dawes, including figures unless otherwise noted
updated: 9/11/13

Unless otherwise specified, this work by Washington State Colleges is licensed under a Creative Commons Attribution 3.0 United States License.

Creative Commons License