Phyghtmap/CartoCSS

This is an example of contours using Phyghtmap and CartoCSS, with following characteristics: - different colors of contours according elevation - different style for minor, medium and major contours - medium and major contours have a elevation label - contours at 0m are skipped

Add in carto the file contour.mss:

@contour-below: #886A08;
@contour-lowland: #0B3B0B;
@contour-highland: #3B240B;
@contour-veryhigh: #0B3B39;

#contours-minor {
    line-width: 0.2;
    [elevation < 0] {
      line-color: @contour-below;
    }
    [elevation > 0][elevation < 2000] {
      line-color: @contour-lowland;
    }
    [elevation >= 2000][elevation < 5000] {
      line-color: @contour-highland;
    }
    [elevation >= 5000] {
      line-color: @contour-veryhigh;
    }
}
#contours-medium {
  line-width: 0.4;
  [elevation < 0] {
    line-color: @contour-below;
  }
  [elevation > 0][elevation < 2000] {
    line-color: @contour-lowland;
  }
  [elevation >= 2000][elevation < 5000] {
    line-color: @contour-highland;
  }
  [elevation >= 5000] {
    line-color: @contour-veryhigh;
  }
}
#contours-major {
  line-width: 0.6;
  [elevation < 0] {
    line-color: @contour-below;
  }
  [elevation > 0][elevation < 2000] {
    line-color: @contour-lowland;
  }
  [elevation >= 2000][elevation < 5000] {
    line-color: @contour-highland;
  }
  [elevation >= 5000] {
    line-color: @contour-veryhigh;
  }
}

#contours-medium-text {
  text-name: "[ele]";
  text-face-name: @book-fonts;
  text-placement: line;
  text-spacing: 500;
  text-size: 7;
  text-fill: #FF0000;
  [elevation < 0] {
    text-fill: @contour-below;
  }
  [elevation > 0][elevation < 2000] {
    text-fill: @contour-lowland;
  }
  [elevation >= 2000][elevation < 5000] {
    text-fill: @contour-highland;
  }
  [elevation >= 5000] {
    text-fill: @contour-veryhigh;
  }
}
#contours-major-text {
  text-name: "[ele]";
  text-face-name: @book-fonts;
  text-placement: line;
  text-spacing: 1000;
  text-size: 8;
  text-fill: #FF0000;
  [elevation < 0] {
    text-fill: @contour-below;
  }
  [elevation > 0][elevation < 2000] {
    text-fill: @contour-lowland;
  }
  [elevation >= 2000][elevation < 5000] {
    text-fill: @contour-highland;
  }
  [elevation >= 5000] {
    text-fill: @contour-veryhigh;
  }
}

Then in project.yaml, we should refer to the new file, in Stylesheet section:

 - "contour.mss"

E.g. after - "ferry-routes.mss"

In the same file, we need to add dabatase access configuration:

 osm2pgsql: &contour
   type: "postgis"
   user: "osmrender"
   dbname: "contours"
   key_field: ""
   geometry_field: "way"
   extent: "-20037508,-20037508,20037508,20037508"

After the section osm2pgsql: &osm2pgsql

In the same file: add the Layer section:

 - id: "contours-minor"
   name: "contours-minor"
   class: ""
   geometry: "linestring"
   <<: *extents
   Datasource:
     <<: *contour
     table: |-
       (SELECT
           way,
           CAST (ele AS INTEGER) AS elevation,
           ele
         FROM planet_osm_line
         WHERE contour_ext='elevation_minor'
         ) AS contours_minor
   properties:
     minzoom: 14
   advanced: {}
 - id: "contours-medium"
   name: "contours-medium"
   class: ""
   geometry: "linestring"
   <<: *extents
   Datasource:
     <<: *contour
     table: |-
       (SELECT
           way,
           CAST (ele AS INTEGER) AS elevation,
           ele
         FROM planet_osm_line
         WHERE contour_ext='elevation_medium'
         ) AS contours_medium
   properties:
     minzoom: 12
   advanced: {}
 - id: "contours-major"
   name: "contours-major"
   class: ""
   geometry: "linestring"
   <<: *extents
   Datasource:
     <<: *contour
     table: |-
       (SELECT
           way,
           CAST (ele AS INTEGER) AS elevation,
           ele
         FROM planet_osm_line
         WHERE contour_ext='elevation_major' AND ele != '0'
         ) AS contours_major
   properties:
     minzoom: 9
   advanced: {}
 - id: "contours-medium-text"
   name: "contours-medium-text"
   class: ""
   geometry: "linestring"
   <<: *extents
   Datasource:
     <<: *contour
     table: |-
       (SELECT
           way,
           CAST (ele AS INTEGER) AS elevation,
           ele
         FROM planet_osm_line
         WHERE contour_ext='elevation_medium'
         ) AS contours_medium_text
   properties:
     minzoom: 13
   advanced: {}
 - id: "contours-major-text"
   name: "contours-major-text"
   class: ""
   geometry: "linestring"
   <<: *extents
   Datasource:
     <<: *contour
     table: |-
       (SELECT
           way,
           CAST (ele AS INTEGER) AS elevation,
           ele
         FROM planet_osm_line
         WHERE contour_ext='elevation_major' AND ele != '0'
         ) AS contours_major_text
   properties:
     minzoom: 9
   advanced: {}

A natural place could be just before id: "roads-text-ref". Note: Bottom layers are drawn on top of previous layers.