Course Notes: Mapping and Map Drafting

Togographic maps - maps which depict the spatial configuration of the earth's surface including hills,
valleys, trees, streams, houses, roads, canals and cultivated areas.

• U.S. Geological Survey

Quadrangle sheets range from:

7 1/2' by 7 1/2' at a scale of 1:24,000 (1:25,000 metric scale), to

4° by 12° at a scale of 1:1,000,000

Source: National Cartographic Information Center, Reston, VA 22092

• Relief Representation

• relief models (cardboard and plastic models)

• shading (visual sensation -- parallel rays of light )

• color

• gradients

• hachures (rows of short parallel lines)

• form line

• contour lines (imaginary lines of constant elevation)

• hypsometric map any map which portrays elevation using one of the previous seven methods

Contour Lines

• Contour imaginary line of constant elevation on the ground surface

Characteristics of contour lines:

1. Horizontal distance between contour lines is inversely proportional to slope.
2. Uniform slopes have uniformly spaced lines.
3. Along plane surfaces, contour lines are straight and parallel.
4. Contour lines are perpendicular to lines of steepest slopes.
5. For summits or depressions, contour lines most close upon themselves.
6. Contour lines, as a rule, do not merge or cross each other.
7. A single contour line can not lie between two lines of higher or lower elevation.

Map Scale

Factors affecting choice of scale:

1. Clarity of features
2. Cost
3. Correlation of map data with other maps
4. Desired size of map sheet
5. Physical factors of features to be shown

Choice of contour intervals,

1. Desired accuracy of elevations on map
2. Features of terrain
3. Legibility of map
4. Cost