Exploring beneath the surface using interactive data transects

ABSTRACT Maps depicting different types of standardized data densities, general ratios/rates, and proportions/percentages are displayed as planimetric projections of continuous or discrete surfaces. However, these standardized data often have sub-layers that are used in compiling a final surface being mapped such as sub-layers stacked on top of one another, or sub-layers used to compute rates and percentages. In this study, we propose an interactive transect tool that allows the user to explore beneath the final surface to describe the patterns of these sub-layers. The tool was developed as a Python add-in for ArcGIS. This package provides two different representations of the cross-sections, a stacked profile tool and a line graph tool, for users to choose based on the type of surface and the purpose of the exploratory analysis. The illustrated applications of the transect tool include exploring the constituent layers of density surfaces, comparing different probability density surfaces, resolving the visual equalization issue for ratio surfaces, and interpreting the spatial patterns of areal classes. An empirical test finds that the transect tool is somewhat more time-efficient than when making visual comparison of values and more accurate in detecting the rank orderings of these values. Overall, it has potential as a visualization tool for multivariate spatial exploratory analysis.