[docs] explicitly document difference between 'rail' and 'train' in transit layer

[matkoniecz]

• What did you see?

https://github.com/tilezen/vector-datasource/blob/master/docs/layers.md#transit-kind-values-line-polygon

Transit line features from OpenStreetMap start appearing at zoom 5+ for national trains, with regional trains addded at zoom 6+. Then subway,light_rail, and tram are added at zoom 10+. funicular and monorail features are added at zoom 12+. Platform polygons are added zoom 14+.

(...)

Transit kind values (line, polygon):

light_rail platform railway subway train tram

• What did you expect to see?

Documentation of difference between rail and train (I guess that it is "Transit line features from OpenStreetMap start appearing at zoom 5+ for national trains, with regional trains addded at zoom 6+", but it is not obvious and even if guess is correct it is unclear which one starts from 5 and which one from 6).

• What map location are you having problems with? City and country are helpful, as well as tile coordinates or latitude / longitude.
• Screenshot? Props for animated gifs.

[nvkelso]

https://github.com/tilezen/vector-datasource/blob/master/yaml/transit.yaml#L23-L34

If a transit route=train also has one of the tags service: [high_speed, long_distance, international] then it'll appear at zoom 5, else the route=train is assumed to be less important and shows at zoom 6 instead.

I don't think we include any railway kind in the transit layer. Are you asking about the differences between railway in the roads layer versus transit layer?

[matkoniecz]

I don't think we include any railway kind in the transit layer.

So mentioning railway in list of "Transit kind values (line, polygon):" at https://github.com/tilezen/vector-datasource/blob/master/docs/layers.md#transit-kind-values-line-polygon is a documentation bug?

[nvkelso]

Yes, this looks to be a documentation problem.

The following should be returned by the YAML, after expanding the inputs to kind: {col: railway}:

bus_stop
funicular
halt
light_rail
monorail
platform
station
stop
stop_area
subway
train
tram
tram_stop

Versus what is documented:

light_rail
platform
railway
subway
train
tram