# In case of categorical cpt, z=value is not applied to the fill of the legend symbol **URL:** \ **Category:** Q&A\ **Tags:** gmt, cpt, legend, color\ **Created:** [July 18, 2024, 7:47am UTC](https://forum.generic-mapping-tools.org/t/in-case-of-categorical-cpt-z-value-is-not-applied-to-the-fill-of-the-legend-symbol/5103 "2024-07-18T07:47:01Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![tllc46](https://avatars.discourse-cdn.com/v4/letter/t/d78d45/32.png) [@tllc46](https://forum.generic-mapping-tools.org/u/tllc46)\ **Post date:** [July 18, 2024, 7:47am UTC](https://forum.generic-mapping-tools.org/t/in-case-of-categorical-cpt-z-value-is-not-applied-to-the-fill-of-the-legend-symbol/5103/1 "2024-07-18T07:47:01Z")
Hello gmt users, I posted this question because I didn’t get the expected results while using gmt’s legend module. According to the legend module manual, the symbol’s fill can be specified by cpt and z=value format. However, in the case of categorical cpt, this method failed. First, prepare the following categorical cpt. ```auto #cpt_file.cpt H red He orange Li yellow Be green B blue C purple ``` And then create a legend file like this: ```auto #legend_file A cpt_file.cpt S - c 0.3c z=H black - Hydrogen S - c 0.3c z=He black - Helium S - c 0.3c z=Li black - Lithium S - c 0.3c z=Be black - Berylium S - c 0.3c z=B black - Boron S - c 0.3c z=C black - Carbon ``` If I run a simple script like this… ```auto #!/bin/bash gmt begin gmt_result png gmt basemap -R0/1/0/1 -JX5c -B gmt legend legend_file -DjRM+w3c+o0.1c -F+p gmt end show ``` ![gmt_result](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/2X/f/fd6ba54ded16f7c1f36e77dac52a9096c5a72ba4.png) As shown in the figure above, only the first fill is correct, but all other fills come out the same as the first fill. A regular cpt like this doesn’t cause any problems: ```auto #cpt_file.cpt 1 red 2 orange 2 orange 3 yellow 3 yellow 4 green 4 green 5 blue 5 blue 6 purple 6 purple 7 purple ``` ```auto #legend_file A cpt_file.cpt S - c 0.3c z=1 black - One S - c 0.3c z=2 black - Two S - c 0.3c z=3 black - Three S - c 0.3c z=4 black - Four S - c 0.3c z=5 black - Five S - c 0.3c z=6 black - Six ``` ![gmt_result](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/2X/7/71b64a961e9658dca5faebb0e22c481ac71f38e7.png) I’m wondering if this is really a bug, or if it’s explained in the manual but I couldn’t find it. My operating system is Ubuntu 22.04 LTS, gmt version is 6.3, and I installed it via apt. ---
**Author:** ![mkononets](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/mkononets/32/4029_2.png) [@mkononets](https://forum.generic-mapping-tools.org/u/mkononets)\ **Post date:** [July 18, 2024, 11:24am UTC](https://forum.generic-mapping-tools.org/t/in-case-of-categorical-cpt-z-value-is-not-applied-to-the-fill-of-the-legend-symbol/5103/2 "2024-07-18T11:24:54Z")
> [@tllc46](#): > > According to the legend module manual, the symbol’s fill can be specified by cpt and z=value format. However, in the case of categorical cpt, this method failed. I think `z=value` only works for assigning numerical `value`s, not string literals like `z=Li` (same true for `ogr2ogr -zfield`) I would also appreciate if `z=value` and the aspatial field assignment in general (`-a=...` worked for string literals, making text labeling and plotting strings easier with `plot` and `text` gmt modules but this is not the case yet. ---
**Author:** ![yvonnefroehlich](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/yvonnefroehlich/32/5064_2.png) [@yvonnefroehlich](https://forum.generic-mapping-tools.org/u/yvonnefroehlich)\ **Post date:** [July 20, 2024, 6:43pm UTC](https://forum.generic-mapping-tools.org/t/in-case-of-categorical-cpt-z-value-is-not-applied-to-the-fill-of-the-legend-symbol/5103/3 "2024-07-20T18:43:59Z")
Maybe setting up a colorbar and using [**-L**](https://docs.generic-mapping-tools.org/6.5/colorbar.html#l) to get separate rectangles can work as an alternative approach here. ```bash gmt begin cat_cpt_cb png gmt basemap -R-5/5/-5/5 -JX5c -B gmt makecpt -C"green,blue,purple,orange,red,yellow" -T0/5/1 -F"+cBerylium,Boron,Carbon,Helium,Hydrogen,Lithium" gmt colorbar -C -DjMR+v+w2c/0.2c -L3p gmt end show ``` ![cat_cpt_cb](https://canada1.discourse-cdn.com/flex047/uploads/gmt/original/2X/9/93bc97a059a7549faee9d2cc2bbed77ab3ff04a4.png) ---
**Author:** ![Esteban82](https://yyz1.discourse-cdn.com/flex047/user_avatar/forum.generic-mapping-tools.org/esteban82/32/54_2.png) [@Esteban82](https://forum.generic-mapping-tools.org/u/Esteban82)\ **Post date:** [July 20, 2024, 10:18pm UTC](https://forum.generic-mapping-tools.org/t/in-case-of-categorical-cpt-z-value-is-not-applied-to-the-fill-of-the-legend-symbol/5103/4 "2024-07-20T22:18:28Z")
> [@tllc46](#): > > First, prepare the following categorical cpt. > > ```auto > #cpt_file.cpt > H red > He orange > Li yellow > Be green > B blue > C purple > > ``` I think this is NOT a CPT. If you run Yvonne command you will get this categorical CPT: ```auto gmt makecpt -C"green,blue,purple,orange,red,yellow" -T0/5/1 -F"+cBerylium,Boron,Carbon,Helium,Hydr ogen,Lithium" 0 green L ;Berylium 1 blue L ;Boron 2 purple L ;Carbon 3 orange L ;Helium 4 red L ;Hydrogen 5 yellow B ;Lithium N 128 ``` ---
**Author:** ![tllc46](https://avatars.discourse-cdn.com/v4/letter/t/d78d45/32.png) [@tllc46](https://forum.generic-mapping-tools.org/u/tllc46)\ **Post date:** [July 22, 2024, 8:19am UTC](https://forum.generic-mapping-tools.org/t/in-case-of-categorical-cpt-z-value-is-not-applied-to-the-fill-of-the-legend-symbol/5103/5 "2024-07-22T08:19:28Z")
Thank you so much for your quick reply. It would be nice if this feature could be officially included in GMT later.