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.
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 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
Figure 6 Cross
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).