Introduction to Topographic Map

Topographic maps are an important tool because they can represent the three-dimensional landscape in two dimensions. On a topographic map, the location of peaks, valleys and saddles can be discovered, apart from other land features.

Significance of Topographic Maps

The topographic map is a two-dimensional representation of the Earth’s three-dimensional landscape.

A topographic map is a detailed and accurate illustration of man-made and natural features on the ground such as roads, railways, power transmission lines, contours, elevations, rivers, lakes and geographical names.

Studying a topo map of a familiar area is a great way to learn how to match terrain features with the contour lines on a map.

Topographic maps give the ability to view a three-dimensional landscape on a twodimensional map. One who is able to read a topo map can identify the elevation and location
of valleys, peaks, ridges and other land features.

Contour Lines

Elevations on a topographic map are marked with contour lines, which connect equal elevation points.

A contour map consists of contour lines for a given geographic region. The contour lines show the topography or the shape of the earth.
To keep the contour map simple and easy to read, not all contour lines are marked with the reading of their elevation. The marked or labelled lines are known as index Contour lines. Index contours are bold or thicker lines that appear at every fifth contour line.

5 Rules of Contour Lines

Rule 1 – every point of a contour line has the same elevation.
Rule 2 – contour lines separate uphill from downhill.
Rule 3 – contour lines do not touch or cross each other except at a cliff.
Rule 4 – every 5th contour line is darker in colour. This is an INDEX contour line.
Rule 5 – Contour lines are closer together in steep terrain and farther apart in flat areas.

Because it’s impractical to mark the elevation of every contour line on the map, the index contour lines are the only ones labelled.

Index lines

Index lines are the thickest contour lines and are usually labelled with a number at one point along the line. This tells you the elevation above sea level.
Intermediate lines are the thinner, more common, lines between the index lines. They usually don’t have a number label. Typically, one index line occurs for every five intermediate lines.
Supplementary lines appear as dotted lines, indicating flatter terrain.

The index contours are a darker or wider brown line in comparison to the regular contour lines.

A contour interval is a vertical distance or difference in elevation between contour lines on a topographic map. The contour intervals are used for calculating the vertical elevation of an area.

Contour lines on a Map

The contour lines show the shape of the earth. Contour lines show elevation and the shape of the terrain. A single contour line marks an equal elevation line, which means that if the contour line measures an elevation of 1,000 M above average sea level, all points along that line are 1,000 M above average sea level.
If the numbers associated with specific contour lines are increasing, the elevation of the terrain is also increasing. If the numbers associated with the contour lines are decreasing, there is a decrease in elevation.
The shape of the contour lines can indicate the shape of the landforms in a specific area. For example, concentric circles show a peak, with the smallest circle marking the summit.
The contour lines next to each other indicate that the land is very steep, while the scattered contour lines show that the land is relatively flat. Therefore, farther the contour lines appear on the map, the smoother the slope of the earth is. The closer the contour lines appear, the
more inclined the terrain will be.

The contour lines surrounding two peaks – or two sets of concentric circles – may indicate the presence of a saddle or space between the peaks.

Contours form closed loops. These loops follow the shape of the land.
The contour lines never cross, as a point on the map cannot have two different elevations at the same time.

Where the contour lines get very close, and almost precipice occurs. If the relief is a vertical cliff, the contour lines almost come together and can look as if they are merging. Cliffs can have one line crossing over the other (this is the only time those lines can cross).

Significance of Contour

It depicts the slope and size of different landforms on map.
It provides a complete and clear image of the land and the surrounding area.
By reading contour intervals it is easy to sort out the different elevations of the landscape.

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