Understanding Elevation and

Derivative Layers

Traditional 2D maps rely on the x- and y-values of latitude and longitude to pinpoint

locations on a flat map. But by adding the z-value of elevation, traditional maps

become 3D maps and can be used to reveal attributes such as hillshade, slope,

and aspect.

ArcGIS offers two image services that enable users to see depth and elevation

above and below the earth’s surface. Terrain is the service for land surface heights

and TopoBathy is the service for water depths.

In this lesson, you’ll use both image services to produce maps showing Mount

Everest in Nepal and the Mariana Trench near the Philippines, the highest and

lowest locations on Earth.

Builds skills in These Areas

➢ Identifying elevation

➢ Understanding hillshade, aspect, and slope

➢ Displaying elevation, bathymetry, terrain, and 3D

Software Requirements

➢ ArcGIS Online account (obtain a free ArcGIS Public Account or ArcGIS trial)

Estimated Time

➢ 30 minutes – 1 hour

Lesson Overview

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Step 1: World Bathymetry Display

The TopoBathy image service combines topography (land elevation) and bathymetry (water depths)

from around the world. Heights are based on sea level and are positively expressed in meters.

Bathymetric values are expressed as negative numbers indicating a direction below sea level.

1. Sign in to your ArcGIS organizational account.

2. On the top ribbon, click Map.

3. Click Add and select Browse Living Atlas Layers.

4. Search for TopoBathy and click the plus button to add the layer to your map.

Exercise

5. Click the back button.

6. Zoom out until you can see the entire Earth.

7. Click Content.

8. Point to the TopoBathy layer and click the Show Legend button.

Q1. What are the lowest and highest elevations shown on the imagery server?

A1. _________________________________________________________

9. Point to the TopoBathy layer, click More Options, and click Image Display.

10. In the Image Display pane, do the following:

• For Renderer, accept User Defined Renderer.

• For Image Enhancement, select Stretch.

• For Stretch Type, select Minimum and Maximum.

• Check the Dynamic range adjustment check box.

• For Color Ramp, click the arrow and select Purple to Green Diverging, Dark.

(Hint: Point to the color schemes and a tool tip appears with the description of the color ramp.)

11. Click Apply and Close.

Step 2: World Bathymetry Structures

By using the TopoBathy image service, you can identify and mark elevation on the map by searching the

map and adding a map note. You’ll start by searching for a location of your choice, whether that’s a

tourist attraction, sports stadium–or even your home.

1. In the search box, type a location you want to plot on your map. (As you type, a list of potential

matches appears; click the one matching your location as soon as you see it.)

2. On the ribbon, click Add and Add Map Notes.

(Alternatively, you can click the Add to Map Notes link in the pop-up.)

3. In the Add Map Notes window, type the name of the location and click Create.

4. In the Add Features pane, click the Pushpin and click the map on the spot representing the location

you chose.

5. In the Points pop-up, do the following:

• For Title, type (the name of your location).

• For Description, type a brief description of your location.

• Click Close.

In the next steps, you’ll create points representing some of the highest and lowest locations on Earth.

You’ll break them down into groups and vary the symbols to distinguish their differences.

6. As you did in the previous steps, use the search bar to locate Mount Everest on the map.

7. After adding a point, in the Points window, do the following:

• For Title, type Mount Everest.

• Click Change Symbol and a red star.

• Click OK and Close.

8. Repeat the process for Aconcagua, Argentina, and Denali, Alaska. Change their symbols to a red

star as well.

9. Repeat the process to create a point for the Mariana Trench, North Mariana Islands. Change the

symbol to a blue diamond.

10. Create points for Dead Sea, Jordan, Lake Baikal, Russia, and Lake Eyre, Queensland, Australia.

Mark these lakes with an orange circle.

11. On the ribbon, click Save and Save As.

12. In the Save Map window, do the following:

• For Title, type Elevations Around the World.

• For Tags, type elevation.

• For Summary, type Location of high and low elevations around the world.

• Save in the appropriate folder.

• Click Save Map.

13. Zoom out so you can see the entire Earth.

Contents now lists 10 layers: one for each of the map notes you created as well as the TopoBathy and

Topographic basemap layers.

Step 3: Derivatives of elevation

In this step, you will use the dynamic Terrain image service, which provides the additional data needed

to derive the values of slope, aspect, and hillshade. Each term, according to the A to Z GIS Dictionary,

differs:

• Terrain–An area of land having a particular characteristic, such as sandy terrain or mountainous

terrain.

• Slope–The incline or steepness of a surface.

• Aspect–The compass direction that a topographic slope faces, usually measured in degrees from

north.

• Hillshade–Shadows drawn on a map to simulate the effect of the sun’s rays over the terrain.

1. In the upper right corner, click New Map and Create New Map.

Note: You may get a warning indicating you have unsaved changes on your Elevations Around the

World map. If that occurs, that means you made some changes to that map before moving on to this

step. Click No, Don’t Open the Map on the warning, click Save again, and then continue with step 1.

Now, you’ll add five layers to your new map. Many of these layers will have like-sounding names in

search results, so you need to ensure you have the correct layer before adding.

2. Click Add and Browse Living Atlas Layers.

3. Search for, and add, the following layers:

• Terrain

• Terrain Slope Map

• Terrain Hillshade

• Terrain Aspect Map

• USA Topo Maps

Note: Focus on the titles during your search; layers are updated periodically, so dates may change.

4. Click the back button and click Content.

The five layers you added completely cover the layers underneath. To know what each layer represents,

you need to uncheck the layer above it.

5. Examine each layer by checking and unchecking layers.

6. In Contents, point to the Terrain layer and, when the cursor turns into a four-way arrow, drag the

Terrain layer to the top.

7. Point to the Terrain layer, click More Options, and click Image Display.

8. In the Image Display pane, do the following:

• For Renderer, verify User Defined Renderer.

• For Symbology Type, verify Stretch.

• For Stretch Type, select Minimum and Maximum.

• For Color Ramp, select the default Black to White color ramp.

• Click Apply and Close.

As in the previous step, you can click the Show Legend button on the layer and see the highest and

lowest elevations.

Q2. What are the highest and lowest elevation levels, expressed in meters, for the Terrain layer?

(Remember: You’re working with a terrain layer, which unlike the TopoBathy layer in a previous step,

does not include ocean depths.)

A2. __________________________________________________________________________

9. Zoom in to Washington state. (If necessary, uncheck all layers so you can see the Topographic

basemap, which shows the state’s boundaries.)

10. After you locate Washington state, check the Terrain layer again so its elevation shows.

Q3. What are the cone-like, white spots in the Terrain layer? (Hint: Uncheck the Terrain layer and zoom

in to those locations.)

A3. ________________________________________________________________________________

11. Uncheck the Terrain layer.

12. On the ribbon, change the Basemap to National Geographic.

Q4. What are the names of two of the Washington state locations with white spots?

A4. ______________________________________________

13. Check on the USA Topo Maps layer and drag it to the top of Contents.

14. Zoom in far enough so that you can see the contour lines.

Q5. How do contour lines represent slope?

A5. ______________________________

15. Check on the Terrain Aspect Map and drag it to the top.

This terrain layer provides a colorized representation of aspect, which is generated dynamically using

the server-side aspect function of the layer. The orientation of the downward-sloping terrain is indicated

by different colors, rotating from green (North), to blue (East), to magenta (South) and orange (West).

In northern climates, aspect is used to show which areas would not receive as much sun. This means

these slopes, because they’re shielded from sunlight, would stay colder and keep their snow coverings

longer. Aspect is also used in vineyard selection because sunlight exposure and angles significantly

impact grape production.

16. Pan and zoom to Greenland, which has a landscape with a distinct aspect.

17. Click any color within Greenland.

Aspects are also expressed in degrees from North. Clicking almost any spot on an Aspect Map opens a

pop-up with aspect and elevation.

18. Close the pop-up.

19. Check on the Terrain Hillshade layer and drag it to the top of the map.

Hillshade is a grayscale 3D representation of a surface based on a solar altitude angle of 45 degrees and

solar aspect angle of 315 degrees. The map provides a quick indication of the shape of the terrain at a

range of map scales.

20. In the search bar, type Mount Saint Helens and press Enter.

21. Close the pop-up.

22. Check on Terrain and drag it above the Terrain Hillshade layer.

23. On the Terrain layer, click More Options and select Transparency.

24. Slide the Layer Transparency setting to 60 percent.

Adjusting the Transparency gives your map a 3D appearance. The farther you zoom in, the more

pronounced the effect.

This image shows the collapsed north face of Mount St. Helens, which unexpectedly erupted on May 18,

1980.

25. Check on the Terrain: Slope Map layer and drag it to the top of Contents.

The layer already comes with the colors showing a colorized representation of degree of slope. Flat

surfaces are gray, shallow slopes are light yellow, moderate slopes are light orange, and steep slopes are

reddish brown.

This Mount St. Helens map shows how the collapsed north face changed the slope of the mountain.

26. Save the map and add appropriate metadata.

Q6. Write a few sentences discussing the benefits of adding elevation to a flat map.

A6. _____________________________________________________________

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l

Q1. What are the lowest and highest elevations shown on the imagery server?

A1. The highest is 8,700 meters and the lowest is -11,000 meters.

Q2. What are the highest and lowest elevation levels, expressed in meters, for the Terrain layer?

A2. The highest is 8,700 meters and the lowest is -450 meters.

Q3. What are the cone-like, white spots in the Terrain layer? (Hint: Uncheck the Terrain layer and zoom

into the areas featuring white spots.)

A3. Mountain peaks.

Q4. What are the names of two of the Washington state locations with white spots?

A4. Mount St. Helens, Mount Rainier.

Q5. How do contour lines represent slope?

A5. The closer the contour lines, the steeper the slope. The more space between contour lines, the gentler

the slope.

Q6. Write a few sentences discussing the benefits of adding elevation to a flat map.

A6. Answers should mention slope, aspect, and hillshade.

Exercise Answers

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About the Author

Kathryn Keranen is an award-winning teacher and author. She

serves as an instructor in geographic science at James Madison

University and is the co-founder of the award-winning Geospatial

Semester. With Bob Kolvoord, she is the co-author of the Making

Spatial Decisions series from Esri Press.

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