GIS 6005 Lab 9: Bivariate Choropleth Mapping

Bivariate choropleth maps provide an efficient way to display two variables and how they are related in a manner that is easy to interpret by the viewer. Like univariate choropleth maps, a bivariate map uses color progression to symbolize classes of data, the difference being its use of two color ramps for two related variables and the combination of those ramps to display the correlation of those variables.

Creating a bivariate choropleth map requires preparation of the data. We first must ensure the data for the two variables are normalized. In the case of the map above, the data for obesity and physical inactivity were already normalized by population. Next, we will create a new field in the attribute table for each variable and populate them with codes for each variable class. To keep the map understandable for the viewer, each variable is generally limited to three classes; this is because the number of classes displayed in the final map is exponential based on the number of classes for the two base variables. Thus, three classes for the two variables equals nine classes in the final map. Four classes for the variables would create a confusing map of 16 classes.

A third field is added to the attribute table and is populated with the concatenation of the two fields created above. This field will be used for the symbology of the final map and represents the combination of the two chosen variables (i.e., obesity and physical inactivity rates). The creation of the color symbology in the above map required some experimentation. The foundation of color choice for bivariate choropleth maps lies in choosing complementary colors for the two variables. Hue, saturation, and value options can then be adjusted for the overlapping classes. Once the symbology is finalized, the legend must be manually adjusted to create a suitable bivariate choropleth legend. This is accomplished by converting the legend to graphics, ungrouping the elements twice, and manually placing the color squares in their final placement. Text elements may then be added to label the legend as is appropriate.

GIS 6005 Lab 8: Analytical Data

Our task this week involved three distinct steps: Downloading and processing raw data, choosing variables that are suitable for comparison and visualization, and creating a map layout to display multiple maps, charts, and text. The data came from www.countyhealthrankings.org and included information on a host of variables broken down by state and county. We first chose two variables we thoughts may be correlated (negatively or positively); I chose obesity and unemployement with the hypothesis that there would be a positive correlation. In order to incorporate this raw data into ArcMap, we created new Excel worksheets containing only the data needed. These worksheets were then used to create charts visualizing our chosen variables. They were also joined to two separate United States maps in ArcMap and symbolized as choropleth maps.

The most difficult part of this assignment, however, was the final task of creating a layout to contain the various maps and charts. I chose to keep the layout as simple as possible with a white background and no neatlines or borders. This allows the viewer's gaze to flow easily from one element to the next. I settled on a tabloid-sized page in landscape orientation in order to stack the two maps on the left and to make room for the charts on the right.

Based on my end product, there does not appear to be a correlation between obesity and unemployment. If a correlation is present, it is relatively minor.

GIS 6005 Lab 7: Terrain Visualization

The various tasks for module 7 have taught us ways to aid map viewers in visualizing the terrain that is being displayed. One of the more precise methods is to display and label contour lines; such maps are familiar to hikers and anyone familiar with USGS map products. Another method is to apply hillshade to a DEM (digital elevation model). Hillshade tools, such as provided by ArcMap, take the elevation data of a DEM and simulate the visual effect of the sun at a specified angle and direction. This visual effect greatly aids the viewer in reaching an intuitive understanding of the topography of the displayed area. Hillshade can be combined with other map elements, such as the above symbology representing tree and landcover types for Yellowstone National Park, to provide the viewer with more information. In this case, the landcover layer is set to a transparency of 30% to allow the hillshade layer to be seen. This gives the viewer an understanding of the relationship between landcover, topography, and elevation that would not be possible if one used hillshade or landcover alone.