How to Learn Topography

Topography is the study of the 3-D shape of the Earth's surface. The word may also refer to the actual relief of a certain area (e.g. "The region has a rugged topography.") Most topographic maps use contour lines to show the shape of the land's surface. Historically, this data was collected by surveyors using instruments such as theodolites and clinometers. This is still done today, but high-tech alternatives such as aerial photogrammetry, which uses two or more pictures taken from different locations to calculate surface altitude, are becoming more prevalent.

Instructions

  1. Understanding Contour Lines

    • 1

      By definition, every point along a contour line is at the same elevation. On any given map, the difference in elevation between adjacent contour lines is set; this is called the "contour interval." In most cases, only some of the contour lines will be labeled with their elevation. To find the elevation of another contour line, simply count the number of contours from the nearest one with a label, and multiply by the contour interval to find the rise or fall in elevation. Here's another way to think about contour lines: if the landscape filled with water up to 100 meters, the 100-meter contour line would perfectly trace the new shoreline. If a point lies between two contour lines, you can estimate its elevation as being between those two elevations.

    • 2

      Because the elevation difference between contour lines is constant, it is very easy to see whether a slope is steep or gradual. The closer the lines are together, the steeper the slope. The side of a mountain might contain a dozen contour lines in the horizontal space of a few meters, while a gently sloping hillside might only have one or two contour lines over the same distance. You can also figure out which way water will flow by looking at contour lines. Water flows downhill, so streams and rivers will always run perpendicular to contour lines. If they are deep enough, their channels should even be visible in the shape of the contours.

    • 3

      Normal contour lines are able to depict nearly all topographic features. The major exception are depressions or ditches, which are totally surrounded by areas of higher elevation. For example, if someone digs a hole at the top of a dome-shaped hill, there is no way to show this with normal contour lines. Depressions such as these are denoted by cross-hatched contour lines, which are also subject to the same contour interval.

    Make Your Own Contour Map

    • 4

      To truly understand topographic maps, it helps to make your own. You can either start with an imaginary map, or do some of your own surveying using a clinometer or a bunyip (see resources) for smaller changes in elevation, or a GPS unit for less precise work. The more points you have an elevation for, the easier it is to draw the contour map.

    • 5

      Choose a contour interval, and begin connecting the dots. Remember, contour lines never intersect. Professionally made or computer-generated contour maps will be more accurate, but you will probably have to estimate. If you have two points, at elevations of 8 and 14 meters, draw your 10-meter contour so that it goes between them and is a little closer to the 8-meter point.

    • 6

      Check your map. Do any of the lines intersect? Are you missing any contours? In other words, if your contour interval is 5 meters, are there two contour lines between the 10-meter contour and the 25-meter contour? Does your map look like the landscape you're describing?