Explaining Topographic Maps

June 21, 2018

Explaining Topographic Maps

topographic map with contour lines - explaining topographic maps

A topographic map of Coopers Rock State Forest, West Virginia. (Photo courtesy USGS)

In the field of Cartography and Geography, there are many different kinds of maps; political maps, physical maps, Topographic maps, thematic maps and general reference maps, each catering to specific needs and uses. Topographic Maps, however, are some of the most useful maps as they visualize the topography/relief of the earth. Topographic maps may seem overwhelming and difficult to understand at first glance, as there appears to be an overabundance of information to take in at once but this doesn’t have to be the case. 

Before we can navigate our way around Topographic maps, we need to understand what exactly a topographic map is. Topographic maps are generally large-scale maps that depict both the physical and man-made features of the landscape; and are distinctly characterized by the presence of contour lines that show the in-detail ground relief of the land. Many man-made features are found on topographic maps, these include roads, rivers, railroads, towns, mountains, elevation and vegetation types(1).

 

 

topographic contour lines

How to use a Topographic Map

 

Knowing what features are generally found on Topographic maps is always handy but the real skill you want, is being able to understand what the map is showing you. This is an invaluable skill that will allow you to adventure into the unknown with nothing more than a paper map and have the confidence to navigate your way through unknown terrain safely. The four main features on Topographic maps that you will need to master are:

  • Contour Lines
  • Map Scales
  • Colours and shading
  • General map details and features[4][5]

 

Contour Lines

As mentioned previously, contour lines are the defining feature of topographic maps - understanding them and how they function is the most crucial part of being able to successfully read a topographic map. Contour lines allow you to visualize the 3D world on a 2D map and identify specific features of the landscape, such as valleys, ridges, slopes, mountains, hills and spurs. This is an essential skill needed when using topographic maps to navigate in the wilderness or areas that lack identifiable man-made features[2].

Explaination of topographic contour lines

How contour lines show a pair of small hills[3]

A Contour line is a line on a map that joins points of equal height above sea level, allowing for an easy visual representation of the height of mountains, steepness of slopes and the general sense of the terrain. The shape of the contour lines is an important piece of information that allows you to identify features on the map such as peaks, ridges, passes or valleys. Smaller circular shapes are most likely showing you peaks or hills, whereas V-shapes are probably showing you a spur or ridge[5].  Slope steepness and rapid elevation changes are indicated by how close the contour lines are to one another, the steeper the slope the closer the contour lines will be together. It must be noted that contour numbers read in an uphill direction, which means the biggest number indicates the top of a hill and the smallest number shows the lowest part of the land. The picture above shows us the link between the shape and steepness of a hill and the contour lines that represent it on a map, as well as the manner in which contour lines are labelled[3].  

topographic map showing the relationship between contour lines

 Contour lines have set intervals of 5m, 10m or 20m depending on the scale of the map. Contour intervals indicate the change in elevation from one contour line to the next and will always remain the same within a map. The contour interval will usually be stated in the map legend. Not every contour line is labeled, on most Topographic maps only every fifth contour line is labeled, these are known as Index Contours, and are indicated on the map by being bolder than the other contours.

Map Scales

Map scale is a very important feature on a Topographic Map, it is the ratio between the distance on the map and the corresponding distance on the ground. Maps come in a variety of scales, with large-scale maps, covering small areas in great detail and small-scale maps covering large areas with little detail[7].

There are a number of ways to represent the scale of a map, with the three most popular being shown in the image below:

  • Bar scale – visually shows the relationship between map and real-world distances
  • Fraction scale – is a ratio, indicating 1 unit of measurement on the map equals 50,000 units in reality
  • Verbal Scale – The scale explains the relationship between the map and real-world measurements.

Scale Bar on a topograhic map

Colours and Shading 

The use of colour in Topographic maps plays a vital role in giving context to the map and its features. Specific colours are given to features and shading is used to indicate the different kinds of landscapes found in the map area.

The colour brown is used to indicate contour lines, green is used to show vegetation, blue is used to indicate water features such as lakes or rivers and black and red are used for man-made features such as roads or administrative boundaries.

 

General map details and features

The map legend allows you to unlock the topographic map as it provides you with all the information you require when trying to decipher the meaning behind all the symbols and colours found on your map. Figuring out what your map symbols mean, allows you to better understand your surroundings when using a topographic map.

 

image of a topograhic map key

 

What are Topographic Maps used for?

In today’s world, Topographic maps have a wide range of uses, from specialized fields such as civil engineering and surveying to recreational uses such as hiking. Most people encounter topographic maps in their recreational lives, when planning a trip into the wilderness or back-country as well as navigating their way around wilderness areas.  

What are you waiting for? Adventure awaits, go outside and explore your world.

 

Sources

  1. https://www.usgs.gov/faqs/what-a-topographic-map
  2. https://getoutside.ordnancesurvey.co.uk/guides/advanced-contours-and-relief/
  3. https://getoutside.ordnancesurvey.co.uk/guides/understanding-map-contour-lines-for-beginners/
  4. https://www.artofmanliness.com/articles/how-to-read-a-topographic-map/
  5. https://www.rei.com/learn/expert-advice/topo-maps-how-to-use.html
  6. http://desktop.arcgis.com/en/arcmap/10.3/map/working-with-text/placing-labels-for-contours.htm
  7. http://geokov.com/education/map-scale.aspx
  8. https://geokult.wordpress.com/2011/09/14/map-symbolisation/

 


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