Category: Imagery

Mathematical relationships among map scale, raster data resolution, and map display resolution

By Dr. A Jon Kimerling, Professor Emeritus, Oregon State University

Resolution Diagram thumb

If you have used any raster data to make maps you may have at one time or another asked yourself, “What is the appropriate resolution of raster data for the map I am making?” This question is tied closely to a basic principle of map compilation that you may have learned in your beginning cartography course: “Always compile your map from source materials of the same or larger map scales”. In our age of digital elevation models and other raster datasets, this basic principle of map compilation can be restated as: “Always create your raster map from data at the same or higher spatial resolution than the ground resolution of your map display grid cells”. The ground resolution of your map display grid cells will depend on the scale of your map. Continue reading

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Symbolizing the hillshade for the World Topographic map

By Charlie Frye, Esri Chief Cartographer

Symbolizing the Hillshade thumb

One of the things I promised myself that I would do last summer was write about some of the key design solutions used in the World Topographic Base Map. Our symbolization of the hillshade is one of the design characteristics that most distinguishes this map. The design intent was two-fold: 1) show shading similar to how hachures were used on hand-drawn maps [to see what I mean one of my favorite 18th century maps depicting the Battle of Bunker or properly Breeds Hill is a good example], and 2) display the low slope areas in white because this creates a ”non-competitive” background for data that is mashed up on this base map. Continue reading

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Hillshades for analysis maps

By Charlie Frye, Esri Chief Cartographer

Hillshades for Analysis Maps Thumbnail

It is often useful to use a hillshade raster to show terrain to support other information in a map such as an analytical surface like population density, or a thematic overlay like soils. There is one significant problem with this; however, which is that the shading from the hillshade modifies the colors of the main information layer making them artificially dark or washed out. That makes map reading and applying what you learn from a legend a frustrating task.

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Hypsometric tinting

By Aileen Buckley, Mapping Center Lead

Hypso Tinting - Thumb

Hypsometric tinting (also called layer tinting, elevation tinting, elevation coloring or hypsometric coloring) is used to enhance elevation zones so map readers can better see differences in relief. You can think of it as “coloring between the lines” where the lines are contours (lines of equal elevation) or isobaths (lines of equal depth below the surface of a body of water). Hypsometric tints are often laid transparently over a hillshaded surface. Continue reading

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Choosing color ramps and displaying for hillshade rasters

By Charlie Frye, Esri Chief Cartographer

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Using ArcMap to symbolize a hillshade raster layer (the output of the Spatial or 3D Analyst’s Hillshade tool) is pretty straightforward, and the default symbology (black to white ramp) doesn’t look too bad. In fact, if your hillshade layer is the only layer in your map, and if you don’t mind not seeing some of the details that have been visually absorbed into the darker tones, the default symbology is okay. To be fair, the default symbology for hillshades is useful for much more than just terrain depictions, so it’s good to know what might be helpful when depicting terrain with a hillshade. The image to the left is an example of a hillshade using the default color ramp. Continue reading

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Setting the Z Factor parameter correctly

By Charlie Frye, Esri Chief Cartographer

Z factor - Thumbnail

We set the Z-Factor parameter based on our latitude.

The Z-Factor parameter is in many Spatial Analyst and 3D Analyst tools; Hillshade and Slope are the two that I use most. Not setting the Z-Factor correctly makes the hillshades look heavy or leaden. It will also make slope values, e.g., for percent slope very small, like 0.00023% – 0.00032% instead of 1.8% to 7.2%.

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