Mapping Center

After seeing my poster that described using dot maps to show soils at the AAG conference in Boston a few weeks ago, Charlie Frye suggested that I write this entry to describe my maps and the technique used to create them.  This seemed especially appropriate given the recent entries in this blog about dot maps. Read More...

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. Read More...

Last week we received an interesting question on Ask a Cartographer about how to create tapered stream or river line symbols. Tapered symbols are actually a bit more complicated than what is shown to the left; those lines are proportionally scaled symbols that are based on an attribute value. Notice that each stream is a single line width.  Tapered symbols would actually change widths along the length of a given feature, giving a very smooth effect. Tapering is more useful for depicting flows that range widely in value or magnitude, whereas proportional symbols are usually an excellent solution for symbolizing rivers and streams. Read More...

In the first dot density mapping blog, we discussed the workflow for creating dot density maps using ArcMap. In that discussion we emphasized the need for using exclusion or inclusion layers. Here is an example of how we set up the inclusion and exclusion choices for mapping population density in San Bernardino County, the county with the largest land area in the conterminous United States. Because of its size and the fact that population is not evenly distributed throughout the county (rather, it is concentrated in the southwest corner, around where Redlands is located), this county exemplifies the limitations of dot density mapping without inclusions/exclusions when mapping population density at the county, the state or even the country level. Read More...

Question: What is the difference between filling a polygon with randomly placed dots and creating a dot density map for the polygon?

Filling a polygon with a certain number of randomly placed dots is a form of choropleth mapping where random dots are the area symbol for a quantity that is assumed to be of uniform density throughout the polygon. The choropleth map seen below of San Bernardino county population density uses random dots in this manner. Read More...

Cynthia Brewer’s new book titled Designed Maps: A Sourcebook for GIS Users is a companion piece designed to compliment the highly successful Designing Better Maps: A Guide for GIS Users published by ESRI Press in 2005. The goal of the book is to offer a graphics-intensive presentation of published maps, providing cartographic details that will prompt GIS users to think about their own maps and how to improve them. Read More...

  There are some general guidelines you can follow regarding size of symbols on a map.  The key is legibility - that is, ability to be seen AND recognized.  Legibility can be affected by: size of symbols and type, Contrasting colors and shapes, Familiarity, Perfect vision and perfect viewing conditions

In relation to size in particular, the ability of an object to been seen from a distance relates to what is called the visual angle – or “a size that subtends one minute of angle (1/60th of a degree) at the eye”.  This is the angle between the light rays from the two ends of the viewed object as they hit the eye, as shown in the figure below. It is usually measured in degrees. Read More...

Symbolizing a hillshade raster layer (the output of the Spatial or 3D Analyst's Hillshade tool) seems pretty straight forward, in fact 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 for far 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. Read More...