extentus

Extentus is a metric used in spatial analysis to quantify the geographic footprint of a phenomenon within a defined study area. It seeks to capture both the spread of occurrences and their concentration by integrating concepts akin to the extent of occurrence and area of occupancy from ecological reporting into a single index. The metric is designed to support cross-region comparisons and temporal tracking where data quality varies.

Origin: The term was proposed in mid‑2010s methodological discussions by researchers exploring unified measures of distribution and has since appeared in ecological and GIS toolkits as an optional footprint index.

Calculation: Extentus is computed from observed occurrences. A boundary is defined (for example, a convex hull). The area of occupancy is the portion of the area covered by nonzero density grid cells. A simple form combines normalized EOO and AOO, for example extentus = w1*EOO_norm + w2*AOO_norm, with weights sum to 1. Some implementations allow alternative boundary shapes or density-based kernels.

Interpretation and use: A higher extentus value indicates a broader and more dispersed footprint, while a lower value suggests focal clustering. It is used in ecology, disease mapping, and planning to summarize spatial footprint, often alongside raw measures and visual maps.

Limitations: Extentus relies on sampling effort, grid resolution, and boundary choice, and comparisons require standardized methods for normalization and weighting. See also: extent, geographic information system, spatial analysis.