Isarithmic Mapping

The focus of the lab this week was isarithmic mapping.  Isarithmic maps depict continuous phenomenon that occur across an area.  The process of interpolation makes it possible for an algorithm to generate data across an entire area even though there are only set locations gathering data..  This type of map is particular common for climatological data and is used in a number of industries such as agriculture and engineering.  

I created a map of the average annual precipitation rates in Washington state using a 30 year data set ranging from 1981-2010.  The interpolation method used on this data was the Parameter-elevation Relationships on Independent Slopes Model, also known as PRISM.  This method takes data from the weather stations and factors in environmental attributes such as elevation and proximity to the coast in order to generate a complete set of data.

To create this map I first map a hillshade effect layer using data from the annual precipitation raster.  This improves the look of the terrain by creating the appearance of depth.  Areas of high elevation tend to have higher rates of precipitation, so this is a logical feature to incorporate into this map.

The next step was to create hypsometric tints.  A hypsometric tint is a set of classed graduated colors useful for showing the range of a environmental phenomenon.  This used the spatial analyst tool "int" to process the annual precipitation raster.  I then symbolized the colors into proper classes that corresponded with precipitation amounts.

The last part of map creation was to create contours.  Contours are lines that show the discrete changes between value ranges.  This process involved the contours tool on the annual precipitation layer at the same values as were assigned for the hypometric tints.  This makes the divisions between the different classes even more obvious.

An isarithmic map of Washington state showing the average annual precipitation rates over 30 years.  The map utilizes hypometric tinting as well as contour lines to display the data.