GUI: Polygon overlays (and underlays)

Since its first release, Biodiverse has supported plotting of polygon and polyline feature class data (from shapefiles).  The support is very basic given users can only plot the outlines of polygons, even though the colours could be changed.  

This has worked well overall, but there are times when the linework from the feature data gets in the way of the cells being plotted.  There are also times when it is useful to plot polygons as solid fills instead of just as the outline.  From version 5 of Biodiverse it is possible to do just this.  

The process is relatively simple.  If a polygon overlay is loaded then it is listed twice in the selection window, once for lines and once for solid fill (with no outline).  The default choice is polylines, which is the current behaviour.  Users then have the option of plotting one overlay above or below the cells.

Colours can be assigned in the usual way.  In this next selection window, the polygon data will be displayed below the cells using a grey colour (grey is quite useful as it does not visually dominate when coloured cells are used).  

Polygon data are displayed as a solid grey fill, under the cells.  In this case it makes it more obvious where there are unsampled regions.  (Cell outlines have also been turned off using the map menu).

Other uses for polygon overlays are in plotting ocean polygons over terrestrial cells to cover over parts of cells that are in the sea (and vice versa for marine data).  

There is no doubt more work to be done, for example plotting more than one layer at a time, but it is a useful improvement.  If more complex plotting is needed then this is when it is best to leverage the power of GIS software.  

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Shawn Laffan

04-Nov-2024

For more details about Biodiverse, see http://shawnlaffan.github.io/biodiverse/  

For a list of some of the analyses Biodiverse has been used for, see https://github.com/shawnlaffan/biodiverse/wiki/PublicationsList 

You can also join the Biodiverse-users mailing list at https://groups.google.com/group/Biodiverse-users or start a discussion at https://github.com/shawnlaffan/biodiverse/discussions