Topographic Map Interpretation

Objectives

To understand and practice the basic guidelines for interpreting a topographic map.

Let's look at some basic guidelines to assist you in interpreting a topographic map.

Basic Guidelines A) Marginal Information Examine the marginal information to gain as much background as possible before becoming involved in the map detail. This background information could include: - map title - map scale - latitude and longitude or military grid - magnetic declination - contour interval Determine what direction is north on the map. If it is not clearly shown, the rule of the thumb is to get the printing right side up so that you can read the majority of information on the map and north is straight up.
B) Broad Patterns Look at the whole map to get a general picture of the area. Watch for broad patterns of land and water, settlements, vegetation, and physical features.
C) Contouring Contour lines are always shown pointing upstream where they cross a stream or river. Steep slope = contour lines close together Gentle slope = contour lines spread out
D) Drainage (The ability of an area to shed water) To help in your understanding of the drainage of an area, ask yourself the following questions: Pattern In which direction do most rivers flow? Do the main rivers run parallel to each other or in some other pattern? Where are the main watersheds? River Valleys How wide is the valley? How deep is it? How steep are its sides? Does the river have a flood plain? What is the valley gradient? Rivers and Streams What is the gradient? Do waterfalls or rapids indicate an uneven gradient? How wide is the river? How many tributaries does it have? Does the river flow relatively straight or does it meander? Is there evidence that the drainage has been altered (i.e. dams)? Surface Water Is there standing water (lakes, marshes, swamps)? If there is a large amount of surface water, does the area have impermeable bedrock? Is the lack of surface water a sign of permeable bedrock?
E) Basic Landforms The shape of contour lines can indicate landforms as shown below. Many of these landforms you may not be familiar with at this time; however you will be by the end of the course.
Courtesy: P. Mleziva
Courtesy: P. Mleziva
Courtesy: P. Mleziva

Courtesy: Geological Survey of Canada

Courtesy: US Geological Survey
F) Nature of Rock Hard (i.e. igneous and metamorphosis) rock and resistant rock generally produce rugged features. Soft rock (i.e. sedimentary) generally produces a more gentle relief.
G) Climate Use information from previous items to make deductions about the climate. The number and size of streams, the vegetation or lack of it, the existence of wells, irrigation ditches or windmills, knowledge of elevation, latitude, etc. should all help.
*H) Land Use* Utilize your knowledge of topographic map symbols to determine activities such as mining, forestry, farming, energy production, urban infrastructure, etc.
I) Cultural Features Place names can often give a clue as to the ethnic groups that have settled an area.
J) Types of Settlement: a) dispersed: houses and other buildings spread out b) nucleated: much development in a small area c) ribbon or strip development: much commercial development (i.e. retail stores) down a particular road/street.
K) Transportation and Communication Look for roads, the density and pattern of the roads, railways, airports, tv towers, radio towers, etc.
L) Forested/Wooded Areas Any area shaded green, unless stated otherwise, is forested/wooded area. White areas are either logged or have no or little vegetation or are used for farming.