What Is Topography? How Is It Used In Site Planning?

A topographic map represents a three-dimensional landscape in two dimensions. It typically shows various landforms, including peaks, valleys, ridges, rivers, and lakes. These maps can also show you whether you will be traveling uphill or downhill on a particular road or trail, showing the steepness, slope, and elevation of the area through topography lines.

Elevations on a topographic map are marked with contour lines (also called topography lines), which connect points of equal elevation. Imagine walking around a mountain in a circle, never going uphill and never going downhill but staying at the same altitude. If you traced the path you walked, you would have a contour line on a map.

Topography lines are typically separated by 40 vertical feet, though you should check the map you're using to be sure, and every fifth contour line is usually marked with an actual elevation.

The shape of the topography lines can tell you the shape of the landforms in a particular area. For example, concentric circles show a peak, with the smallest circle marking the summit. Contour lines that are close together indicate that the land is very steep, while contour lines that are spread apart show that the land is relatively flat. 

Reading a topographic map doesn’t just help you understand elevation and landforms. It can help you to deduce the soil type, ground conditions, and stability of any area by looking at those elevations and landforms. Where does all that rain go? It doesn't just stay up on that mountain top. How does that effect the soil below? All of these details make up the topographical picture of the land on which we build our homes and businesses.

As such, from a site planning perspective, topography helps to determine whether a property is suitable for a particular type of building and where the best place for the structure to go is. 

There are a few different ways and combinations you can use to find the topography of a site, including:

• Topographic maps: As we mentioned above, topographic maps give great insight into a given terrain and can help determine the type and quality of the soil.

• Aerial photography: High resolution aerial photographs and satellite imagery will show the topography of a site from above.

• GPS surveys: This isn’t a DIY approach because you need specialist equipment but this technique involves using GPS receivers to determine precise locations and elevations, and then representing those either on a map or digital elevation model (DEM)

• Mobile mapping systems: Again, this is more of a professional technique. It involves mountain mobile mapping systems onto a vehicle or drone to capture data while moving through the site. An accurate 3D models of the terrain can then be developed.

Of course, the other options is to hire site plan designers who will include the topography of the site.

Notice the topography lines in this image? The lines that are closer together indicate a steeper elevation and the lines farther apart indicate a wider plain.

So, the next time you step onto the road less traveled, you may start to see those rolling hills, valleys, and streams a bit differently and understand how every elevation and even the soil might affect your next building project.