Cartography, Module 6 - Isarithmic Maps

Greetings all,

There's several topics and discussion points to get after understanding the map below. In unexplained terms we can throw together the following: interpolation, continuous, hypsometric, contours, and hillshade to name most of them. Learning and employing these terms, and how to employ the concept they represent is the subject of this map. Lets look at those first before we get to the map below.

Interpolation... or how we take known data points and then provide a smooth surface of data points for the areas between known points. In the map belows case, the method of interpolation is called PRISM (Parameter-Elevation Regression on Independent Slopes Model). This model prioritizes elevation but takes into account major terrain and other factors which affect climate patterns. It takes the known data points and weighs it against all other locations and associated terrain to create a value for all other locations. This looks at the relationship between precipitation, elevation, and landscape changes, including slope, rain shadowing, and difference between leeward and windward sides of the mountainous areas.

Continuous vice Hypsometric Tints. Continuous tone symbology is one of the two types of symbology approaches we discuss in this module that are appropriate for smooth, continuous data phenomena such as rainfall which is the subject of the map below. The approach applies a shaded or colored tone corresponding to the data value of each pixel. This continuous scale provides smoother appearance than hypsometric tinting, because it is not stepped. Hypsometric tinting is the other method of symbolization discussed in this module which is appropriate for isarithmic maps which again revolve around smooth, continuous phenomena. This approach enhances the ability to visualize 3-D surfaces with color schemes that are stepped or associated with a classed range of values. This can be used with or without contour lines. Within the final map there are numerous classes of data but the baseline color scheme is the same as that above, dark for drier areas, green – blue for wetter areas.

The other thing not yet discussed is contouring and hillshade effect. The map below has contour lines to help break out the hypsometric color classes, and has an overlying hillshade effect which is designed to provide a greater sense of the elevation relief of the region. 

As you can see, the subject area is Washington State, and this map breaks out precipitation by average over a 30 year period. Note the stepped approach to showing the different inch classes of rain fall. The shadows within the map are the added hillshade effect to help highlight the terrain relief. You can see that this method helps highlight these mountainous areas where rainfall is concentrated. 

Thank you.

v/r

Brandon