Currently the layer cannot be selected for low zoom levels.

It would be useful if a missing property in the config file fell back gracefully to the default value, rather than killing the process with a hard error.

Is there any appetite for such a change? We could potentially specify default values in a json file that the C++ code reads at compile time and the python script valhalla_build_config parses at runtime?

Here's what I did

 [-0.0743414, 51.5015841],
 [-0.05273140000000039, 51.46430039999999],
 [-0.0531279, 51.4637