INTERPRETATION OF PHYSICAL FEATURES ON TOPOGRAPHIC MAPS
The interpretation of topographic maps means identifying, describing and explaining the features which are represented on the maps by symbols. This is an important exercise in map reading which calls for a mastery and careful study of the contour pattern, that is their spacing and values which enable the students to identify the various relief features.
Landforms on a map are commonly identified through contours. This is because contours are drawn in different shapes and forms. They vary in their degree of closeness. Therefore the closer and more winding the contours are, the steeper, rougher and rugged the relief of that area is and the wider apart and less winding the contours are, the gentle or calmer the relief region is.
Relief features can be classified under two groups, that is, those that belongs to highlands and those that belongs to lowland region.
Relief features and landforms likely to be found on highland regions for purpose of identification and description include; plateau, escarpment, ridge, valley, conical or flat top hill. While those landforms or features commonly found in a lowland region include; plain, broad river valley, undulating hills, coastal areas with coastal features like promontories, sand spit, and bars, beaches, cliff, wave-cut platform, lagoons, tombolo etc.
It is very important for students to know how to go about describing each of these in order to present the relief of the area exactly how it looks like. topographic commentary or description is done with a lot of precision using the appropriate technical vocabulary. However, it is very unlikely that all of the upland and lowland features can be found in a map.
For convenience of the exercise, Students are advised to divide the map into physical regions, before they start to describe the land forms found in it.
Description of upland features
- Check whether there is a mountain or hill on the map and if yes.
- Locate or states the area on the map where it is found example NW, NE, SW, SE, or east of the map.
- Estimate the area occupied by this mountain or hill on the map.
- Indicate the highest and lowest points on the upland and also the average height.
- What range of height is shown between the mountain or hill top and valley bottom.
- Are there many changes of height within the upland.
- Describe the nature of the mountains or hills say whether they are conical or flat top hills.
- Describe the nature of the slopes. State whether they are concave, convex, gentle, regular or irregular slopes
- The part of the map where the plateau is found.
- The approximate area of the map it occupies.
- Say whether the plateau is dissected or not. If plateau is dissected, rivers will cut through it.
- State the uniformity or evenness of its surface.
- Describe the general height of the plateau and mention the highest point on it.
- State the part of the map on which the escarpment is found.
- Estimate the area of the map occupied by escarpment.
- State the orientation of the escarpment.
- State the height of the escarpment using contours values, spot height or trigonometrical station.
- State the highest and lowest points of escarpment.
- Say whether or not the escarpment is dissected ie having rivers flowing on it like the Bamenda escarpment.
- Describe the nature of its slope.
- The area of the map which the ridge is located.
- Describe the approximate area of the map occupied by the ridge.
- Describe the orientation or alignment of the ridge.
- Describe its height and say whether the top of the ridge has been cut into separate hills by cols, saddle or passes.
- describe the nature of the slope, steep, dip or scarp slope.
- Say whether rivers have cut deep valleys into the sides of the ridge or not.
- Ask your self whether there is a lowland on the map. this will enable your search for it. If yes.
- Where is it found on the map.
- Find out whether there are some hills on the lowland or not.
- What type of low land coastal, plain, broad river valley etc.
- How much area of the map does it cover.
- What is the shape of the lowland, flat, gently sloping, undulating etc.
- what is the general height of the low land.
- Is there any valley on the map? If yes.
- Where is it located on the map.
- Is it a dry valley or river valley.
- What is the general trend or orientation of the valley.
- What are the characteristic of the valley broad, narrow, steep sided or has gentle slopes on both sides.
- What is the nature of the slopes; concave, convex, regular etc.
In order to describe coastal scenery, candidates must make sure that there is a sea on the map and they must have a good knowledge of coastal geomorphology, this is because the coast has unique features.
The coast is that land immediately bordering the sea. In considering coastal features two sets of features come to mind, that is features that result from coast of emergence and feature that result from coast of submergence. all of these result from change in the land and sea levels such that they either become depressed or uplifted.