Focusing on feature-based differences in map comparison

Differences between two maps can be quantified using any cartometric summary; of these, feature-based statistics are potentially more relevant than pixel-based statistics. Distributions of feature areas and shape indices from the workshop maps were compared using a classic information theory index. To place differences in a significance context, uncertainty about cartometrics that arise from both the form of data model and mapping function are considered. Data model characteristics such as raster cell size, raster origin and attribute membership functions can generate variation without the existence of feature differences in the actual surfaces. Stochastic simulation can represent uncertainty due to the mapping function. An understanding of the end-to-end map generation process, absent in the workshop example, can help build a description of its space of uncertainty so that cartometric quantities can be meaningfully compared.