# Coloring OGR\_GMT polygon files based on attribute column **URL:** \ **Category:** Q&A\ **Created:** [December 15, 2020, 5:06am UTC](https://forum.generic-mapping-tools.org/t/coloring-ogr-gmt-polygon-files-based-on-attribute-column/1129 "2020-12-15T05:06:54Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![weiji14](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/weiji14/32/33_2.png) [@weiji14](https://forum.generic-mapping-tools.org/u/weiji14)\ **Post date:** [December 15, 2020, 5:06am UTC](https://forum.generic-mapping-tools.org/t/coloring-ogr-gmt-polygon-files-based-on-attribute-column/1129/1 "2020-12-15T05:06:54Z")
Given an [OGR\_GMT](https://docs.generic-mapping-tools.org/6.1/cookbook/ogrgmt-format.html) with a “placename” and “zattribute” consisting of two triangular polygon areas like so: ```auto # @VGMT1.0 @GPOLYGON # @Nplacename|zattribute # @Tstring|double # FEATURE_DATA > # @D"Area 1"|0.70 # @P 1 5 1 3 3 3 > # @D"Area 2"|0.80 # @P 3 3 5 3 5 1 ``` I can plot the polygons ok using `gmt plot tmp.gmt -Baf -L -png map`: ![map](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/1X/20dd3d6b34eb86dc7a0112bb9cff99af9288f865.png) But how can the triangles be colored individually based on the “zattribute” column? I tried looking at the `-a` (aspatial) column in [`plot`](https://docs.generic-mapping-tools.org/dev/plot.html) but couldn’t seem to get this to work: ```bash gmt plot tmp.gmt -Baf -L -Cbatlow -G+z -azattribute -png map # plot [WARNING]: Mismatch between actual (3) and expected (2) fields near line 6 in file ``` I saw the answers at [https://flint.soest.hawaii.edu/t/fill-in-polygon-color/322/4](https://flint.soest.hawaii.edu/t/fill-in-polygon-color/322/4) and [https://flint.soest.hawaii.edu/t/coloring-polygon/1026/2](https://flint.soest.hawaii.edu/t/coloring-polygon/1026/2), but here I don’t have `> -Z0.7` in the multisegment header (difficult to assign it to many polygons at once, but open to ideas of bringing the “zattribute” to the `> -Z` header if anyone has ideas). ---
**Author:** ![pwessel](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/pwessel/32/30_2.png) [@pwessel](https://forum.generic-mapping-tools.org/u/pwessel)\ **Post date:** [December 15, 2020, 7:00am UTC](https://forum.generic-mapping-tools.org/t/coloring-ogr-gmt-polygon-files-based-on-attribute-column/1129/2 "2020-12-15T07:00:42Z")
Think you need to use **-aG=zattribute** and no -G+z See the various tests under gmt/test/ogr ---
**Author:** ![weiji14](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/weiji14/32/33_2.png) [@weiji14](https://forum.generic-mapping-tools.org/u/weiji14)\ **Post date:** [December 15, 2020, 11:10am UTC](https://forum.generic-mapping-tools.org/t/coloring-ogr-gmt-polygon-files-based-on-attribute-column/1129/3 "2020-12-15T11:10:11Z")
Close! The [gmt/test/ogr/lookup.sh](https://github.com/GenericMappingTools/gmt/blob/bb0b2d9dd69a4ab537fc1b0353b5ba5f78b777c0/test/ogr/lookup.sh#L40) example was using RGB colour (e.g. 110/186/103), so not quite right in this case as it gave black coloured triangles `gmt plot tmp.gmt -Baf -Cbatlow -L -aG=zattribute -png map`: ![map](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/1X/dbca208e71de1fe0843a4b025e2ac4a9e4e336fc.png) I had a dig around and saw this question [https://flint.soest.hawaii.edu/t/how-to-extract-attribute-values-from-shapefile-for-cpt-file-generation/464](https://flint.soest.hawaii.edu/t/how-to-extract-attribute-values-from-shapefile-for-cpt-file-generation/464), and `-aZ=zattribute` seemed to do the trick: `gmt plot tmp.gmt -Baf -Cbatlow -L -G+z -aZ=zattribute -png map` ![map](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/1X/0a2566c418966ecf6ab1ebe577921373df9fa5d1.png)