Docker Build Checklist

[knutole]

• fix need to npm install mapnik --build-from-source manually (in pile)
• remove apt-get dependencies, as they're too flimsy to ensure stable build
• create build-proof fork of mapnik @ systemapic/mapnik
• add CI test to all builds
• separate wu and pile deps (ie. gis:latest). no need to have mapnik in wu, no need for phantomjs in pile, etc. both should be leaner builds.
• remove postgres/postgis from gis build
• create much cleaner gdal build