Topographical and geological maps

Topographical maps show features seen from above the earth surface whereas geological maps give us information about beneath the earth surface.

What is a topographical map?
A topographical (topo means top) map is a map that depicts the shape of the land seen from above. Topographical maps usually show contour lines (elevation above sea level), lakes, rivers, roads, forested areas, urban areas and the like.

What is a Geologic Map?
Geologic maps are not like other maps. They show geological features like rock formation indicated by contact lines where different geologic units are found next to each other.
Faults are great cracks or fractures on the earth crust. They occurs when the ground is being stretched apart. Then, when the fault breaks, it allows land to slip downwards as seen in Figure 1. A further break of the fault produces shock waves that causes the earth to shake and the result is an earthquakes.

Geologic units that are bent and warped into rounded wavelike shapes (crest Figure 2 and trough Figure 3) are called folds.

In the Learning Resource Center you find a variety of topographical and geological maps. Study some of them and familiarise yourself with the features that are of interest to building studies.

Topographic Maps
Particular features can be recognised from the contour pattern, thus allowing a mental picture of the topography to be constructed. Studying the natural features such as rivers, lakes, marshes, cliffs and coasts, which are shown in topographic maps, helps to identify the hills and valleys which together form the topography of an area.

Geological Maps
Geological maps show the distribution of the superficial deposits (glacial sands and gravel, boulder clay, alluvial sands and gravel etc.) and the underlying solid rocks at the earth's surface. The distribution of the solid rocks in a particular region is shown by means of geological boundaries, drawn as lines in the geological map.

Figure 4 Topographic Map Figure 5 Geological Map

Figure 6 Cross Section

Cross-section A-B

Geological maps are generally accompanied by vertical cross-sections, a stratigraphic column, a legend or key showing the structural symbols, ornament and colours used on the map, and a brief description of the geology. Vertical cross-sections are drawn across the map to illustrate the geological structure of the rocks, as shown in the opposite cross-section (Figure 6).