Using topographic maps to study landforms has been a key part of Geography and Earth Science instruction for over a century. It has never been easier to do, thanks to the seamless USGS topographic maps for the USA and the base topographic map for the world available in ArcGIS Online. I have created a set of 12 questions and a map containing 20 landforms as a starting point for these investigations.
Remember the old days when the landform you were seeking to analyze seemed to inevitably fall across corners of 4 topographic paper map sheets? The USGS maps, originally published at 1:24,000, 1:100,000, and 1:250,000 scales, display seamlessly in ArcGIS Online – no more corners! The map above opens to the Ennis, Montana area, on the classic alluvial fan that has long been a staple with these sorts of investigations.
Questions include the following, which can be used as is or as a springboard for your own questions.
Use the bookmarks to zoom to the 1:24,000-scale map. Measure the distance between each contour line. Determine the contour interval by reading the numbers on the contours. Calculate the slope in percentage and in degrees. Calculate the slope of the fan again using the 1:100,000 scale map. Is this measurement different than the measurement you calculated using the 1:24,000 scale map? Explain a few reasons for possible differences. Calculate the slope in another location on the fan. Is the slope similar to your other reading? Why are slopes so constant on an alluvial fan?
Calculate the area of the alluvial fan using the square mile grid shown on the topographic map as a guide, and the scale bar in the lower left of your ArcGIS Online map window. Then compare this measurement against what you get by using the measure tool above the map. Be sure to indicate the units you are using. Name 3 differences in the type and number of features shown on USGS maps at the 3 different scales. Why do these differences exist?
Examine the following features, each of which is accessible through the Bookmarks above the map. For each landform, indicate: What is the name of the landform? What is the location of the landform? How did the landform form? What did the landform and area look like 100 years ago? 1000 years ago? Why? What will the landfrom and area look like 100 years from now? 1000 years from now? Why? Would you classify the landform as rapidly changing or slowly changing? Why? How has the landform influenced human activity and settlement in this area? How have humans modified the landform, if at all, in this area? What is the climate and vegetation like in this area? Can you find the same landforms in other areas? If so, where are they?
The 20 landforms included in the map and lesson are a tombolo, a col, a salt dome, lava beds, marine terraces, the Llano Estacado, sand hills, drumlins, moraines, a caldera, an estuary, karst, a water gap, a tarn, an arete, a structural dome, a slow moving landslide, trellis drainage, an oxbow lake, and an inselberg. The lesson also includes comparison of landscapes shaped by the public land survey system, long lots, and metes and bounds.
You can use ArcGIS Online to draw your own points, lines, and areas on the topographic map using “Add” and “Create Editable Layer.” Link your features to text, photos, and videos. Save your map (requires either a personal or an organizational ArcGIS Online account). You can also add USGS topographic maps to any ArcGIS Online map through the “Add” function by searching for “USA Topo.” You can also use the Add tool to add climate, weather, ecoregions, and other layers to help you understand the interaction between climate and landforms.
Working outside the USA? Then make sure your base map is set to “Topographic” and you can explore landforms using a topographic map base all around the world!