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GEOLOGICAL SURVEY CIRCULAR 368

FEATURES SHOWN ON

TOPOGRAPHIC MAPS

UNITED STATES DEPARTMENT OF THE INTERIOR

Douglas McKay, Secretary

GEOLOGICAL SURVEY

W. E. Wrather, Director

GEOLOGICAL SURVEY CIRCULAR 368

FEATURES SHOWN ON TOPOGRAPHIC MAPS

By John B. Rowland

Washington, D. C., 1955

Free on application to the Geological Survey, Washington 25, D. C.

GEOLOGICAL SURVEY

TOPOGRAPHIC INSTRUCTIONS

Chapter 1 B 3

FEATURES SHOWN ON TOPOGRAPHIC MAPS

Contents

Abstract .............. .

Principles of map representation

1. Definition of a n1ap • •

a. Topographic map . . . . . . . . . b. Planimetric map .....

2. Elements of map construction .

a. Colors and classes of features . . b. Lines and symbols . . .... c. Letters and numbers . . • . . d. Map scale . . . . . . . . . . .

3.. Problem of selecting features .

4. Selecting map features for a purpose

5. Other factors in selecting map

Page 5 5 5 5 5 5 5 6 6 6 6 6 features. . . . . . . . 7 a. Legibility . . . . . . 7 b. Cost of production . . . . . 8 c. Obsolescence . . . . . . . . . 8 d.

Concept of a landmark 8

Map delineation of topographic relief 8 6.

Methods and objectives 8

a. Measurement . . . . . . . . . 9 b. Interpretation . . . . • . . . 9

7. Selection in mapping relief features . 9

a. Choosing a contour interval 9 b. Generalization . . . . . . . . 10

8. Topographic expression 10

9. Kinds of relief features 10

a. Erosional features . . . b. Residual features ... c. Depositional features . .

10. Symbols and patterns used to show

relief ....... . 10 12 12 12 a. Hachures . . . . 12 b. Area patterns . . 12 c. Relief shading. . . . 15

Map representation of water features . 15

11. Periodic changes in water features . 15

a. Classification of water features . 16 b. "Normal" water level ...... . 16 Page

Map representation of water features--Continued

12. Kinds of water features and map

symbols . . . . . . . . . . 16 a. Linear watercourses . . • . . . 16 b. Area water features. . . . . . . 17 c. Glaciers and permanent snow fields •....•. d. Springs and wells . e. Coastal features . •

Manmade map features . . •

13. Coordinate systems, subdivisions,

and boundaries . . . • . . . a. Coordinate systems • • • • b. Public-land subdivisions c. Boundaries . . . . . • . .

14. Travel and transportation routes .

a. Roads and trails . • . b. Railroads .•..•... c. Other route features

15. Buildings and cities ..

a. B11ildings ..•.. b. Building groups . . c. Towns and cities

16. Names, notes, and numbers •

a. Map names . • • • . • . b. Geodetic control marks . c. Spot elevations •....

Information on map margins . • .

17. Identification, orientation, and

explanation . . . • . • . . a. Identification . . . . . . b. Responsibility, methods, and dates • . • . • . • ••• c. Scale, contour interval, and other data ..•

Map references • . • . . . . .

18. Special selected list .

19. Other reference maps

17 17 17 18 18 18 18 19 19 19 19 19 19 19 20 20 20 20 20 21
21
21
21
21
21
22
22
23
3

Figure 1.

2. 3. 4. 5. 6. 7. 8. 9. 10.

Pictographic map symbols

Comparison of map scales

Illustrations

Contours. . • . • • • . • . • . • .. Two maps of identical areas in southeast New York State •.• Con toured slopes • • . • • • • • • . . . • . • .

Drumlins in northern New York .•.

Cedar Creek alluvial fan in Montana .

Depression contours and hachures ..

Hydrographic features. • . • . • • • • . • • • .

Information shown in

center of lower margin. Topographic map symbols . . . . . . . . . . . . . . . . . 4 Page 6 7 9 11 13 14 15 16 17 22
facing page 22

Chapter 1 B 3

1

FEATURES SHOWN ON TOPOGRAPHIC MAPS

ABSTRACT

Topographic

maps represent features on the earth's surface by means of symbols and labels; separate colors distinguish the main classes of map features. The amount of information shown on a topographic map depends on the map scale, the purpose of the map, and the cost of obtain ing the information. This chapter describes the three main categories of map information and the methods by which they are shown. Reference lists of published maps and a chart illustrating standard map symbols are included.

PRINCIPLES

OF MAP REPRESENTATION

1. Definition of a map

A map is a graphical representation, at an established scale, of a part of the earth's sur face, showing important natural and manmade features in their correct positions relative to a coordinate reference system and to each other. a. Topographic map. --A topographic map, as distinguished from other kinds, portrays by some means the shape and elevation of the ter rain. Geological Survey topographic maps usu ally represent elevations and laNdforms--the shapes into which the earth's surface is sculp tured by natural forces--by contour lines. Other features are shown by a variety of conventional signs, symbols, lines, and patterns, which are printed in appropriate colors and identified by names, labels, and numbers. The chart facing page 22 shows the standard symbols used on the topographic maps of the Survey. b. Planimetric map. --A planimetric map is similar to a topographic map, except that it does not portray relief in a measurable form.

The Survey publishes some planimetric maps for

use until they can be replaced by topographic maps.

1The number

1 B 3 signifies Book 1, Part B, Chapter 3 of the

Geological Survey looseleaf manual of Topographic Instructions. For a table of contents, see Chapter 1 A 2 (Circular 92).

2. Elements of map construction

A topographic quadrangle map is the prod

uct of both engineering and the graphic arts.

Surveys made on the ground and from photographs

are organized in a coherent form and reproduced graphically according to a plan. To be useful the map must present information legibly. The graphic accuracy must be consistent with the accuracy of the source surveys and with the pub lication scale. The map must include the infor mation essential to its purpose and must exclude nonessentials. The main -elements of quadrangle map construction have been formulated to attain these objectives. a. Colors and classes of features. --The information shown on the quadrangle map is divided into three general classes, each printed in a different color. Information about the shape of the land surface--hypsographic or topographic information--is printe'd in brown. Water fea tures--hydrographic information--are shown in blue. Cultural features--manmade objects·- are shown in black. The system of division is not precise. Some manmade features--for ex ample, levees and earth dams--are also topo graphic features and are printed in brown, ·not black. 5

6 (Ch. 1 B 3) TOPOGRAPIDC INSTRUCTIONS

Besides the colors used for the three main

classes of features, green is used to show wood land--timber, brush, vineyards, and orchards- and red is used to show public-land subdivisions (cultural features) and the classification of the more important roads. b. Lines and symbols. --Linear features are represented by lines of various weights and styles (solid, dashed, dotted, or some combina tions). Structures, or individual features, are portrayed by a system of pictographs or symbols.

The symbols originated as plan views of the ob

jects they represent, and they retain something of this character although they are now formal ized. The building symbol, for example, is a solid or open square. The railroad symbol is a line with evenly spaced cross ties. The dam and levee symbols look approximately like dams or levees as seen from the air. (See fig. 1. ) D j ( ////I I\\\'\.'\ II

BUILDINGS DAM

RAILROAD LEVEE

Figure 1. --Pictographic map symbols.

c. Letters and numbers. --Because lines and symbols cannot represent map information completely, they must be supplemented by the names of places and objects. Notes must be added to explain some features that cannot be depicted clearly by symbols alone. In mapping topographic features the information portrayed by contour lines must be supplemented by eleva tion figures. Letters and numbers are essen tial to map interpretation, but they tend to ob scure other map information. Therefore, they must be selected and positioned carefully on the map so that interference with other detail is kept to a minimum. d. Map scale. --Map scale is the relation ship of the size of the map to the size of the ground area it represents. The relationship may be expressed as a linear equivalent, such as 1 inch equals 1 mile--meaning that 1 inch measured on the map represents 1 mile on the ground--or it may be expressed in many other ways. The scale of Survey maps is given in the form of a ratio or fraction, without dimensions; the numerator is the distance on the map, and the denominator is the corresponding distance on the ground.

For example, 1:24,000 means that

one unit of length on the map represents 24,000 similar units on the ground. 3.

Problem of selecting features

The amount of information that can be de

picted legibly on a map is limited by the scale of the map. The effect of scale on map content is emphasized if the scale is considered as a ratio of areas rather than a ratio of distances.

Figure 2 illustrates the actual paper areas rep

resenting 1 square mile at 2 standard scales for topographic mapping.

The major problem in map compilation is

to make the best use of the available map space.

The space cannot be crowded with lines and

symbols beyond a definite limit without making the map unreadable, yet the amount of informa tion that might be useful or desirable is almost unlimited. The cartographer must select the features that are the most valuable to the map user. The smaller the map scale, the more critical and difficult the problem of selection becomes.

4. Selecting map features for a purpose

Topographic maps are often made for a

particular purpose. For example, a map made

FEATURES SHOWN ON TOPOGRAPHIC MAPS (Ch. 1 B 3) 7

I sq mi at 1=24 000

I sq mi at 1=62 500

Figure 2. --Comparison of map scales.

for the purpose of designing a new highway would show the type of woodland cover and the classifi cation of soil and rock along the route. Informa tion about drainage, property lines, and buildings would be shown in detail as required. The map would be in the shape of a strip and would cover a relatively small ground area. This type of map is called a special-purpose map because it has limited value for other uses.

Unlike special-purpose maps, the quad

rangle maps produced by the Geological Survey have been designed to be used for many purposes.

Scales, contour intervals, accuracy specifica

tions, and features that are shown on the maps have been developed gradually over a period of years to satisfy the requirements of government al agencies, industry, and the general public.

Because these maps serve a wide variety of

uses--scientific, engineering, military, and ad ministrative--they are called general-purpose maps.

Changes in symbolization and in features

to be shown are adopted only after careful con sideration of their effect on the various map users, as well as the operational problems and costs involved in making the changes. Changes in symbolization usually are submitted to a gov ernmental interagency Committee on Map Sym bols for review and approval.

5. Other factors in selecting map features

The functions the map is intended to serve

determine the features that it is desirable to map, but other factors must be taken into ac count before it is decided what features actually can be shown. Among the most important con siderations are legibility, the cost of compiling the information, and the permanence of the map ped features. a. Legibility. --The requirement that map information be legible and easily read means that small map features must be represented by symbols larger than·the true scale size of the features. Roads, for example, are shown

90 feet wide on 1:62, 500-scale maps despite the

fact that most roads are not actually this wide.

Buildings and other structures also are shown

by minimum-size symbols that may be larger than the actual scale size of the buildings. On aerial photographs at the same scale as the map, which show all features at true scale size, small features sometimes are not visible without magni fication.

8 (Ch. 1 B 3) TOPOGRAPHIC INSTRUCTIONS

Symbols larger than scale size take up

extra map space; therefore, where small features are close together, all of them cannot be shown.

Generally, the less important features are omit

ted in congested areas. b. Cost of production. --The extent to which some kinds of map features are shown is deter mined partly by the cost of compiling the informa tion. Aerial photographs are the source of most map information, but features that cannot be identified on mapping photographs must be obtain ed by field methods, a procedure that is relative ly more expensive. As an example, not all sec tion corners are mapped; they are too small to be seen on aerial photographs, and the cost of map ping all of them by field surveys would be exces sive. c. Obsolescence. --Not only the original cost but also the cost of keeping the map up to date is considered in deciding what features to map.

Generally, the more features depicted, the

more quickly the map becomes out of date. Cul tural features are especially subject to change.

If the maps are to have a reasonably long useful

life, the features portrayed must be restricted, to some extent, to relatively permanent.objects. d. Concept of a landmark. --Many kinds of features are shown on some maps, although omitted from others, because of the landmark character of the features. In this sense, a land mark is an object of sufficient interest in relation to its surroundings to make it outstanding. For example, buildings may be considered landmarks when they are used as schools or churches or when they have some other public function. They may be landmarks also because of their outstand ing size, height, or design; or they may be land marks because of their history, such as old forts or the birthplaces of famous men.

The same principle is applied to features

other than buildings, but the adjacent area always is considered in relation to the object. Where map features are few, objects that would not be shown in more congested districts may be map ped as landmarks.

MAP DELINEATION OF TOPOGRAPHIC

RELIEF

6. Methods and objectives

Contour lines are the principal means used

to show the shape and elevation of the land sur face. Other means are spot elevations and hachures and pattern symbols for special kinds of relief features that are not suited to contour ing. Relief information is printed in brown on topographic maps.

Con tours are lines connecting points of

equal elevation. They always are continuous lines, and, if the map is large enough, they re turn to the points of beginning to form closed loops. A contour may be variously defined as--

An imaginary line on the ground, every point

of which is at the same elevation above a specified datum surface (mean sea level for topographic maps of the Survey). A level or grade line.

A line of constant elevation.

A coastline or shoreline of level water.

An assumed shoreline resulting from the

assumed rising of a body of level water.

However it is defined, a contour is the

line traced by the intersection of a level surface with the ground. A series of contours is traced by a series of level surfaces, a different contour for each elevation. Contours are illustrated in figure 3. Each contour line on the map repre sents a definite ground elevation measured fromquotesdbs_dbs14.pdfusesText_20

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