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Analysing spatial point patterns in R - CSIRO

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130<br />

1.1 Types of data 7<br />

The mark could be multivariate (for example, a tree could be marked by its species and its<br />

diameter) or even more complicated.<br />

1.1.3 Covariates<br />

Our dataset may also <strong>in</strong>clude covariates — any data that we treat as explanatory, rather than<br />

as part of the ‘response’. Covariate data may be of any k<strong>in</strong>d. One type of covariate is a <strong>spatial</strong><br />

function Z(u) def<strong>in</strong>ed at all <strong>spatial</strong> locations u, e.g. terra<strong>in</strong> altitude. Such functions can be<br />

displayed as a pixel image or a contour plot:<br />

elevation<br />

120 130 140 150 160<br />

140<br />

130<br />

125<br />

145<br />

145<br />

135<br />

140<br />

150<br />

130<br />

elevation<br />

135<br />

150<br />

155<br />

140<br />

135<br />

125<br />

130<br />

130<br />

Another common type of covariate data is a <strong>spatial</strong> pattern such as another <strong>po<strong>in</strong>t</strong> pattern,<br />

or a l<strong>in</strong>e segment pattern, e.g. a map of geological faults:<br />

Copyright<strong>CSIRO</strong> 2010

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