Nearest Neighbour Analysis (NNA)

The study of settlements in order to discern any regularity in spacing by comparing the actual pattern of settlement with a theoretical random pattern.

The straight line distance from each settlement to its nearest neighbour is measured and this is divided by the total number of settlements to give the observed mean distance between nearest neighbours. The density of points is calculated as:


Where Rn is the nearest neighbour index. An index of 0 indicates a completely clustered situation. 1 shows a random pattern, 2 a uniform grid, and 2.5 a uniform triangular pattern. The interpretation of index values can be difficult since these values are not part of a continuum.

A technique for examining the spatial distribution of two-dimensional recorded points, for example settlement sites within a river catchment. Assuming that all the points to be examined are contemporary and that all relevant examples are known, a series of statistics can be calculated by measuring the linear distance between sites. This can very easily be done using a GIS system. A nearest-neighbour index (usually denoted by the symbol R), is calculated from the ratio of the average observed distance from each point in the pattern to its nearest neighbour, to the average distance expected if the pattern were randomly distributed, which depends solely on the density of the pattern being studied. The index R varies from 0.00 for a totally clustered pattern through 1.00 for a random distribution to a maximum of 2.15 for a completely regularly spaced pattern.

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