Locate train station forecourts

There does not seem to be any explicit tag to delineate a station forecourt.

Station forecourts can be readily recognised by a person looking directly at OpenStreetMap, so, in principle, it should be possible to detect them. I've called this type of implicit feature in OSM 'emergent data' - other examples include urban areas, drainage basins, tree-lined streets etc.

Typical forecourts will be adjacent to the main entrance of the station and are likely to represent the area between that entrance and the nearest adjacent public road (i.e., excluding footways, cycleways, pedestrian areas and service roads). They are also likely to contain bus and/or tram stops, taxi ranks, bicycle parking, disabled parking or access, passenger drop-off points, information boards/maps etc.

Unfortunately not all the features needed to readily identify forecourts are mapped consistently. Ideally the main entrance would be mapped as a node of the station building or station area (although small stations without a building are unlikely to have a forecourt). In lieu one can find footways entering the station building, and define the points where they intersect the building as entrances but then one needs to identify the main entrance.

So in summary: at present finding them will require a fair amount of clever processing of OSM data.

You can also encourage the OSM community to map (or likely tag) more station entrances and perhaps suggest an explicit way of marking forecourts (try the tagging mailing list).