GME

Geospatial Modelling Environment

mergesampleplots (Merge Sample Plots)

Merges sample plots based on the area of suitable habitat within plots so that resulting plots contain a minimum area of suitable habitat to sample

Description

The purpose of this tool is to merge sampling plots (and/or zones) that contain less than a specified area of suitable habitat. It is designed for use with plot and zones layers that have been created with the genregionsampleplots command. This tool can also be applied to a plot layer that has no corresponding zone layer. The difference is that when a zone is also specified, merging of plots occurs preferentially within the same zone.

It is essential that you specify the zone and plot layer that were created simultaneously using the genregionsampleplots tool. If you have run that tool more than once, you must not mix a zone and plot layer from different sessions (the unique ID values are unlikely to match and this will result in this merging tool producing nonsensical data). It is also not advisable to use a previously merged zone/plot layer as the input to this tool.

Define the minimum suitable habitat area in coordinate system units – e.g. square meters for UTM. This value corresponds to the values in the ArSuitHab field that were produced by the genregionsampleplots command. Any zones with a value of ArSuitHab less than the value specified will be merged using the merging rule you specify. When a plot is merged, the attribute fields are updated and the polygon it has been merged with is deleted. Note that the new, merged plot is not evaluated to determine if the minimum suitable area criteria has been met. However, this merged polygon is available for other plots to be merged with. Note that after merging the plot ID’s will still be unique, but may not be a consecutive series as some of the plots have been deleted. After the plots are merged, the zones are evaluated for merging. If a zone is merged then the plots that are contained within this zone are updated to reflect the new zone ID value.

Merging Rules. For all merging rules the term neighbour refers to the four bordering plots in the four cardinal directions. A plot on the edge of a zone, however, will have fewer than four neighbours because merging of plots across zones is not permitted.

1. Dominant Neighbour Rule. The plot (or zone) is merged with the neighbour that contains the greatest total area of suitable habitat (the maximum ArSuitHab value).

2. Longest Border Rule. The plot (or zone) is merged with the neighbour that shares the border passing through the greatest amount of suitable habitat. The line representing the shared border is intersected with the suitability raster and the proportion of suitable habitat cells intersected by that line is calculated. The border with the greatest value defines which polygons are merged.

3. Simple Contiguity Rule. The plot (or zone) is split into halves: north and south halves, and east and west halves (i.e. two pairs of halves, not four quarters). The half containing the greatest proportion of suitable habitat defines the neighbour that is selected for merging.

In landscapes in which the suitable area is highly fragmented, the Dominant Neighbour Rule is probably the best choice.

Syntax

mergesampleplots(in, out, area, rule, [inzones], [outzones], [areazones], [rulezones], [raster]);

inthe input plot data source that was created using the genregionsampleplots command (it must contain a ArSuitHab field)
outthe new, merged, output plot data source
areathe minimum area of suitable habitat per plot (identifies the plots that will be merged)
rulethe number representing the plot merge rule: 1=Dominant Neighbour, 2=Longest Border, 3=Simple Contiguity (see full help documentation for details)
[inzones]the input zone data source that was created using the genregionsampleplots command
[outzones]the new, merged, output zone data source
[areazones]the minimum area of suitable habitat per plot (identifies the plots that will be merged)
[rulezones]the number representing the zone merge rule: 1=Dominant Neighbour, 2=Longest Border, 3=Simple Contiguity (see full help documentation for details)
[raster]a suitability (1/0) raster that is used to characterize plots, required for rules 2 and 3 (see help documentation for further details)

Example

mergesampleplots(in="C:\data\plots.shp", out="C:\data\plotsmerged.shp", area=2500, rule=2, raster="C:\data\suit.tif");

mergesampleplots(in="C:\data\plots.shp", out="C:\data\plotsmerged.shp", area=2500, rule=1, inzones="C:\data\zones.shp", outzones="C:\data\zones.shp", areazones=25000, rulezones=1);

mergesampleplots(in="C:\data\plots.shp", out="C:\data\plotsmerged.shp", area=2500, rule=3, inzones="C:\data\zones.shp", outzones="C:\data\zones.shp", areazones=25000, rulezones=3, raster="C:\data\suit.tif");


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