Vélosm

Introduction

Trying to build a nice map for everyday cyclists.

To achieve that, we have at least the following goals:

• Make streets less visible that aren't cycliste friendly
• Exagerate relief data to know when it's going to be hard (or fun)

Getting things running

We use TileMill http://mapbox.com/tilemill/ to configure the rendering of the map.

If you create a directory in ~/Documents/MapBox/project/ containing the project.mml and style.mss files. Edit project.mml to set the different sources (we will have to improve this!).

StreetData comes from OpenStreetMap, imported with http://imposm.org into a http://postgis.refractions.net/ database.

At last, elevation data comes from the Shuttle Radar Topography Mission (SRTM)

Elevation

Most instructions are based on : http://mapbox.com/tilemill/docs/guides/terrain-data/

We used GDAL (http://www.gdal.org/) to convert those elevation data.

1. Get elevation data as a tiff file http://srtm.csi.cgiar.org/

2. Reproject into the "google"-projection:

   glwarp -s_srs EPSG:4269 -t_srs EPSG:900913 srtm_37_03.tif projected_srtm.tif::
   

3. Generate a hillshade file. It will cast a shadow on one side of the hills. We use -s 0.2 to exagerate the shading:

   gdaldem hillshade -s 0.2  -co compress=lzw projected_srtm.tif hillshade_srtm.tif
   

4. Generate a file that indicates steep slopes:

   gdaldem slope projected_srtm.tif slope_srtm.tif
   

5. However, we want some colors to that. We say that flat is white, 5° orange and 10° red. So we write a file slope_ramp.txt containing:

   0 255 255 255
   5 255 127 0
   10 255 0 0
   

6. We generate the file with colors:

   gdaldem color-relief -co compress=lzw slope_srtm.tif slope_ramp.txt slope_srtm_color.tif
   

7. We might also want some elevation contour, at 10 and 50 meters:

   gdal_contour -a elev projected_srtm.tif contour10.shp -i 10.0
   gdal_contour -a elev projected_srtm.tif contour50.shp -i 50.0
   

When importing the raster layers (slope_srtm_color.tif and hilshade.tif), we need to specify the following styles in order to have a better interpolation and to merge the layers:

#hillshadesrtm, #slopesrtmcolor {
          raster-scaling: bilinear;
          raster-comp-op: multiply;
}