Exercise 9: Principles of Cartography
List the main steps for preparing a contour map,
illustrate by figures?
1.
Divide
the area into small portions e.g. grids (cells) for sampling (why sampling)?
2.
Take
measurements of elevation at the center of each cell using Surveying techniques
(level, total station)
3.
Determine
the minimum and maximum values of the elevation and the contour interval (CI).
CI depends on the purpose of the map and scale. For example, for engineering
projects (buildings, dams) small CI is recommended e.g. 2-5 meters, for large
areas large CI can be used e.g. topographic map of a country CI can be 20,50,
100, etc.
4.
From
the minimum and maximum values of the elevation and the contour interval (CI),
the number of contours can be determined
5.
Interpolate
the unknown values for each contour
6.
Draw contour smoothly
Illustrate by figures: How the contour map for the following features appeared:
River:
contours pointing to the source (>)
Mountain:
Increasing upward
Depression
(lake): increasing downward
Cliff:
Contours overlap each other
Sharp
slope: Contours are very close to each other
Gentle
slope: Contours not too close to each other
Flat
areas: Contours are equally spaced
