Styling a raster layer

Raster layers are composed of a grid of values in one or more bands. A grayscale image will have a single band, with each grid element containing the intensity at that pixel. An RGB image will have 3 bands, corresponding to red, green, and blue values. A raster can have any number of bands.

This raster layer has a single band. With the default raster symbolizer, it is drawn as a grayscale image.

Viewing the existing style

  1. In the layers tab of Composer, click the style option for the dem layer to go to the style edit page. A simple default style is already associated with this layer:

    name: raster
    feature-styles:
    - name: name
      rules:
      - symbolizers:
        - raster:
            opacity: 1
    
    ../../../_images/raster_dem_gray.png

    Default raster display

Adding contrast

  1. If we want the land to show up better in the display, we can use the contrast-enhancement attribute:

    name: raster
    feature-styles:
    - name: name
      rules:
      - symbolizers:
        - raster:
            opacity: 1
            contrast-enhancement:
              mode: histogram
              gamma: 4
    

    This adjusts the contrast so each brightness level contains an equal amount of content, and darkens the resulting image by a factor of 4.

    ../../../_images/raster_dem_contrast1.png

    Added contrast

Creating a color map

The color-map attribute can be used to convert any single band of data into a colored image based on the band values.

  1. Since contrast-enhancement cannot be used with color-map, remove it from the style. Replace it with a color map with the following intervals:

    Color Values
    '#0043C8' Less than 8080
    '#00C819' Between 8080 and 100000
    color-map:
      type: intervals
      entries:
      - ['#0043C8', 1, 8080, blue]
      - ['#00C819', 1, 100000, green]
    
    ../../../_images/raster_dem_interval.png

    Interval color map

  2. The color map can also be used with type: ramp to create a gradient of colors between entries. Use this to create a basic colored elevation map with entries denoting ocean and four elevations:

    Color Value
    '#0043C8' (ocean) Less than 8080
    '#3A3519' (shore) Between 8080 and 8100
    '#4B4422' (low elevation) Between 8080 and 10000
    '#857B54' (mid elevation) Between 10000 and 15000
    '#D9D1A8' (red) Between 15000 and 30000
    color-map:
      type: ramp
      entries:
      - ['#0043C8', 1, 8080, ocean]
      - ['#3A3519', 1, 8100, shore]
      - ['#4B4422', 1, 10000, low]
      - ['#857B54', 1, 20000, mid]
      - ['#D9D1A8', 1, 60000, high]
    

Final style

The final style looks like:

name: raster
feature-styles:
- name: name
  rules:
  - symbolizers:
    - raster:
        opacity: 1
        color-map:
          type: ramp
          entries:
          - ['#0043C8', 1, 8080, ocean]
          - ['#3A3519', 1, 8100, shore]
          - ['#4B4422', 1, 10000, low]
          - ['#857B54', 1, 20000, mid]
          - ['#D9D1A8', 1, 60000, high]
../../../_images/raster_dem_brownscale.png

Simplified color map

We have now styled all of our layers. Continue on to Composing a map for the final step in the process.