An Incremental and Philosophically Different Approach to Measuring Raster Patch Porosity

Tarmo Remmel

doi:10.3390/su10103413

Abstract

A new method for measuring the porosity of individual 2D raster patches in a GIS for characterizing the combined complexity of a shape’s edge in conjunction with its internal perforations is developed. The method is centered on comparing the number of cellular edge–edge joins relative to the theoretical maximum number of similar joins possible given a set number of cells comprising a landscape patch. As this porosity (Φ) increases, the patch (or shape) can be viewed as deviating from a maximally compact form, comprising higher edge complexity and internal heterogeneity (inclusion of perforations). The approach is useful for characterizing shapes for which a simple perimeter- or area-based metric misses the internal complexity and where the porosity of the patch may provide insight into spatial processes leading to the development of the landscape fabric. I present theoretical results to illustrate the mechanics of the approach and a small case study of boreal wildfire residual vegetation patches in Ontario, where real resulting wildfire process-driven landscape patches are assessed for their porosity at five spatial resolutions. The results indicate that naturally occurring and unsuppressed boreal wildfires in the study area typically produce residual vegetation patches with an average porosity of 17.6%, although this value varies slightly with the spatial resolution of the data representation.

Highlights

Mapping land cover and its changes is central to landscape analyses and for establishing baseline conditions, formulating hypotheses of landscape change, and understanding processes of transition, disturbance, or landscape alteration
While numerous metrics exist across the three levels of measurement, the number of patch-level metrics pales in comparison to the others, and lacks a metric focused on the structural level of individual patch-forming cells
This paper focuses solely on the concept of two-dimensional porosity, considering the representation of spatial phenomena stored in a geographic information system (GIS)

Summary

Introduction

Mapping land cover and its changes is central to landscape analyses and for establishing baseline conditions, formulating hypotheses of landscape change, and understanding processes of transition, disturbance, or landscape alteration. The identification, measurement, and quantification of shapes and characteristics of individual landscape elements (hereafter referred to as “patches”, to follow terminology borrowed from landscape ecology) that can be subsequently summarized across a wider extent if required, rather than the production of single metric values for landscapes or classes that dilute the infinite complexity of an entire landscape [36] are gaining attention.

Results

Conclusion