Mapping Center : Creating an elevation legend

Friday, July 24, 2009 7:40 PM - makella

Creating an elevation legend

Elevation Legend thumb

A common question that we get on Mapping Center is how to create an elevation legend in ArcMap. In September of 2007, there was a blog entry on Mapping Center (Creating a legend for hypsometrically tinted shaded relief) that outlined a method for creating a legend for hypsometrically tinted shaded relief. When that blog was written, the option to Convert Graphics to Features was not yet available. This blog outlines a simpler method for creating an elevation legend using this new option (version 9.3 and later).

Creating a graphic for the legend
To use the Convert Graphics to Features Option, you have to be in Data View. On your completed map, choose a location where you want your elevation legend to appear, and draw a rectangle using the New Rectangle tool on the Draw Toolbar.
Converting the graphic to a feature
Once you have created your graphic rectangle, select it and then right click on the name of the active data frame and select the Convert Graphics to Features option. Use the option to use the same coordinate system as the data frame, and specify the output location of the feature class. You can also check the option to automatically delete graphics after conversion, or you can delete it manually once the features have been created.
Click OK and choose the option to add the exported data to the map as a layer.
Symbolizing the legend
You will need two copies of the converted graphic feature class for your legend. The bottom copy will be symbolized the same way you symbolized the hillshade on your map (this usually involves only specifying the color ramp), and the top copy will be symbolized the same way you symbolized the layer tint on your map (this usually involves specifying the color ramp and the amount of transparency).
In the Table of Contents, right click the feature class, click Properties and click the Symbology tab. Click the color patch and then click the Properties button in the Symbol Selector dialog to get to the Symbol Property Editor. Here, change the Type to Gradient Fill Symbol and leave the default Style as Linear. Select the same color ramp you used to symbolize your hillshade. Change the Intervals to 100, the Percentage to 100, and the Angle to -90. (This is if you are creating a horizontal legend – the angle would be 0 if you were creating a vertical legend.) Click OK twice and then click Apply to see the changes. Check to make sure that the darker color is on the bottom and the lighter color is on the top – if they are reversed, go back and change the Angle to 90. Otherwise, click OK.

Once you have this feature class symbolized, right click it in the Table of Contents and click Copy. Then right click on the name of the data frame and select Paste Layer(s).
Now right click the top copy and click Properties. On the Display tab, change the transparency to the same transparency level as the layer tint on your map (in our case it was 40%). Then on the Symbology tab, click on the symbol patch and click Properties. Select the same color ramp you used for your hypsometric tint. and change the Angle to 0. (If you are creating a vertical legend, the angle would be 90.) Click OK twice and then click Apply. Check to make sure that the lower elevation colors are on the bottom and the higher elevation colors are on the top – if they are reversed, go back and change the Angle to -90. Click OK to keep these changes.
Adding the legend text
At this point, you can switch to Layout View to add the text to your legend. There are two options for creating the text for your elevation legend. Both use the New Text Tool on the Draw Toolbar and both will place the text in an annotation group. The difference is that you can choose to associate the text with the legend feature class so that if you turn this on or off in the Table of Contents, the text will also turn on or off.
With the first option, you simply place the text in an unfocussed data frame. With the second option, you create the new annotation target and you specify that this is where you want the text to go. Then you place the text in a focused data frame.
To use the second option, in the Drawing menu located on the Draw Toolbar, select New Annotation Group. In this dialog box, specify a name for the new annotation group (for example, "Legend Text"), and then select the Associated Layer (the feature class that you created when you converted the graphic rectangle to a feature). You can also set a reference scale and scale range, if you want. Click OK to accept your selections.

Before you place your text, double click your data frame in layout view so it becomes focused (you will know it is focused when you see hashed lines around the frame of your map).
Click on the Drawing menu of the Draw Toolbar and under the Active Annotation Target make sure your newly created annotation group is checked on. You can then begin using the New Text tool to add the elevation values and units of measurements to your map. When you are done, you can check that this works right by turning off the legend layer in the Table of Contents – the legend text should also turn off.