# GMT.jl : Coloring lakes, keeping oceans bathymetry
**URL:** https://discourse.julialang.org/t/gmt-jl-coloring-lakes-keeping-oceans-bathymetry/135163
**Category:** Geo
**Tags:** gmt
**Created:** [January 20, 2026, 4:14pm UTC](https://discourse.julialang.org/t/gmt-jl-coloring-lakes-keeping-oceans-bathymetry/135163 "2026-01-20T16:14:06Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@Balinus](https://discourse.julialang.org/u/Balinus)
#### Post date: [January 20, 2026, 4:14pm UTC](https://discourse.julialang.org/t/gmt-jl-coloring-lakes-keeping-oceans-bathymetry/135163/1 "2026-01-20T16:14:06Z")
Hello! I’m trying to plot some points over a map. I would like to keep the default topography/bathymetry visuals, but the lakes are “green”, being over 0m at sea level (my guess). Here’s my current code. I tried to use the `coast` function, but it overrides the ocean visuals.
```julia
using GMT
grdimage("@earth_relief_01m", proj=(name=:lambertConic, center=[-97.5 48], parallels=[40 50]), region=(-140,-55,32,64), coast=true, show=false)
GMT.coast!(water="skyblue", shore=true)
GMT.plot!(station, marker=:circ, ms=0.23, mc=:white, markeredgecolor=:red, fmt=:png, figname=joinpath(repfig, "stations_NA.png"))
```
This gives the following figure:
While, if I omit the `coast` function, it gives a nice ocean visuals:
```julia
grdimage("@earth_relief_01m", proj=(name=:lambertConic, center=[-97.5 48], parallels=[40 50]), region=(-140,-55,32,64), coast=true, show=false)
GMT.plot!(station, marker=:circ, ms=0.23, mc=:white, markeredgecolor=:red, fmt=:png, figname=joinpath(repfig, "stations_NA.png"))
```
Which gives the following (lakes are green)
I tried inverting the call of `coast` and `grdimage` without success.
Thanks!
---
### Author:  [@joa-quim](https://discourse.julialang.org/u/joa-quim)
#### Post date: [January 20, 2026, 9:18pm UTC](https://discourse.julialang.org/t/gmt-jl-coloring-lakes-keeping-oceans-bathymetry/135163/2 "2026-01-20T21:18:54Z")
The key here is to understand that coastlines in GMT are a set of polygons with different hierarchical levels (see brief [here](https://www.generic-mapping-tools.org/GMTjl_doc/documentation/modules/coast.html#gshhg-information)) and option `area`. Together, we can split it in to calls. The first plots only the coastlines and the second plots only the lakes and hence we paint/pen style them differently. See
```julia-auto
grdimage("@earth_relief_01m", proj=(name=:lambertConic, center=[-97.5 48], parallels=[40 50]), region=(-140,-55,32,64))
# Plot only the ocean-land interface (polygon level 1)
coast!(shore=true, area=(0,1,1))
# Plot only the coast-lakes interface (lakes are polygons level 2)
# The the 200 means that polygons with area < 200 km2 are nor drawn)
coast!(shore=true, water=:red, area=(200,2,2), show=true)
```
---
### Author:  [@Balinus](https://discourse.julialang.org/u/Balinus)
#### Post date: [January 21, 2026, 6:05pm UTC](https://discourse.julialang.org/t/gmt-jl-coloring-lakes-keeping-oceans-bathymetry/135163/3 "2026-01-21T18:05:33Z")
> [@joa-quim](#):
>
> ```julia-auto
> grdimage("@earth_relief_01m", proj=(name=:lambertConic, center=[-97.5 48], parallels=[40 50]), region=(-140,-55,32,64))
>
> # Plot only the ocean-land interface (polygon level 1)
> coast!(shore=true, area=(0,1,1))
>
> # Plot only the coast-lakes interface (lakes are polygons level 2)
> # The the 200 means that polygons with area < 200 km2 are nor drawn)
> coast!(shore=true, water=:red, area=(200,2,2), show=true)
>
> ```
Thanks! I works very well:
```julia
grdimage("@earth_relief_01m", proj=(name=:lambertConic, center=[-97.5 48], parallels=[40 50]), region=(-140,-55,32,64))
coast!(shore=true, area=(0,1,1))
coast!(shore=true, water="skyblue", area=(200,2,2), show=false)
GMT.plot!(station, marker=:circ, ms=0.23, mc=:white, markeredgecolor=:red, fmt=:png, figname=joinpath(repfig, "stations_NA3.png"))
```
---
### Author:  [@joa-quim](https://discourse.julialang.org/u/joa-quim)
#### Post date: [January 21, 2026, 8:20pm UTC](https://discourse.julialang.org/t/gmt-jl-coloring-lakes-keeping-oceans-bathymetry/135163/4 "2026-01-21T20:20:16Z")
Just two quick notes.
One do not normally need to set `show=false` because that is the default for almost all functions (so that we can overlay like in current example). The exceptions are the `viz` function that is meant to be a quick visualizer ad hence has the `show=true` by default. Other exceptions are the demo functions like [seismicity](https://www.generic-mapping-tools.org/GMTjl_doc/documentation/modules/seismicity.html) and alike.
Adding `shade=true` to the `grdimage` command makes an even nicer image (IMO).
---
### Author:  [@Balinus](https://discourse.julialang.org/u/Balinus)
#### Post date: [January 21, 2026, 8:22pm UTC](https://discourse.julialang.org/t/gmt-jl-coloring-lakes-keeping-oceans-bathymetry/135163/5 "2026-01-21T20:22:23Z")
Thanks, I will try!
---
### Author:  [@Balinus](https://discourse.julialang.org/u/Balinus)
#### Post date: [January 22, 2026, 1:10pm UTC](https://discourse.julialang.org/t/gmt-jl-coloring-lakes-keeping-oceans-bathymetry/135163/6 "2026-01-22T13:10:42Z")
I agree that it is much better with the `shade=true` option!
---
### Author:  [@joa-quim](https://discourse.julialang.org/u/joa-quim)
#### Post date: [January 22, 2026, 2:06pm UTC](https://discourse.julialang.org/t/gmt-jl-coloring-lakes-keeping-oceans-bathymetry/135163/7 "2026-01-22T14:06:22Z")
Nice. And actually I over complicated this issue. There is an option in `coast` exactly for this (`river_fill`) but its long names parsing is broken, so one must use _condensed_ syntax. The two `coast!` calls above can be replaced by a simpler:
```julia-auto
coast!(shore=true, area=200, river_fill="skyblue+l")
```
and when a fix is committed, that can be expressed as:
```julia-auto
coast!(shore=true, area=200, river_fill=(lake=true, fill=:skyblue))
```