The User's Needs when Zoomed In: What is a general user looking for if they access a web map of this station? If they are zoomed in close then chances are they are searching to answer these questions:
- Where is a station entrance with temporary parking? - I want to drop off someone by car.*
- Where is a station entrance handy for me? - I'm getting to the station by bus/bike/foot?*
- Where do I find food/drink/toilets/cash machine?
If they are changing trains at Clapham they will probably follow the station signs rather than looking at a web map so 'where is the platform I need?' doesn't get onto the list.
Entrances and Exits are Key: So from a user's point of view I think the primary information that a map of this scale should show are the station entrances and exits. If the user question is  then they still want to know about exits/entrances since often services are ouside the station and they will have to get in and out. Using the above list it seems to me that the map could also usefully show temporary parking, bus stops, cycle racks, food outlets, toilets and cash machines. However, the symbols showing these services should be secondary in visual impact to the entrances.
Let's see how the map providers fare in meeting these user needs:
Entrance locations: Before we begin the review we need to understand a little about the entrances to the station. On the Open Street Map below I have added the four entrances to the station as red squares. Its also important to know that the Brighton Yard entrance (bottom) is relatively new compared to the others.
Open Street Map of the Station:
First up, Open Street Map is packed with detailed information. All the entrances are marked except Brighton Yard, however, they are symbolized weakly as dotted red lines and are difficult to pick out. Services are marked on the map at many locations although I note that food outlets on the platforms and the access bridge are missing (I've now added them myself, because that's the point of Open Street Map). There is no opportunity to click symbols and access further information.
Whilst Open Street Map has done well in terms of having the information available, my problem with this map is that it shows too much. Most of the information is there but by packing all the data onto the map it becomes visually complex and the entrances are not emphasized. A particular problem is the rail tracks: all the lines and sidings are shown but the location of these has no use for the average user as they will be navigating within the station guided by signs within the station. Also, the dashed line symbolisation just doesn't work when the lines are packed together.
I discussed the 'too much' information problem in a previous post.
Google's Map of the Station:
Google's map is far clearer when compared to the Open Street Map but important information is missing and the symbolisation is confusing. It shows roads and bus stops clearly but other services aren't well marked. Entrances to the station are missing. The multiple rail lines have been reduced to two which show the general directions of the lines leading out from the station - much better symbolisation.
My main problem with this map is that rather than use a polygon and a single marker to show the station (see last weeks discussion), Google has a confusing group of 3 markers. You would be mistaken for thinking the station was quite small and in three separate locations. In fact it's one large station that covers most of the above map, as you can see from the Open Street Map. Click the rail station symbol and you are not linked to anything to do with the station but see information about the nearest buses. Very odd.
Bing Map of the Station:
Bing's map is similar to Google's in terms of clarity: Few train lines are shown, roads are clear and easy to see. Bing also uses a single marker at the main St John's hill entrance which is logical and an improvement on Google's map. When clicked this station symbol links to a route calculator which is more sensible.
However, the other entrances are not marked and no services are marked. At this zoom level I would expect at least some services marked and the lack of entrances is a real issue.
Conclusion: I've outlined why I think at this scale of map, the key information users need about Clapham Junction station is the location of the entrances. The maps vary in how many entrances they mark but none of them show all of them with the required level of emphasis IMHO.
Looking at other data that could be usefully marked on the map; Open Street Map has the most detail but it is presented in a visually complex way. Bing maps goes to the other extreme with a very clear map but showing little useful information. Google's approach of mixing some service information on a relatively clear map represents the most sensible approach but they have used some very odd symbols in the process.
*Obviously 'entrance' could be replaced by 'exit' in these questions for journeys going in the other direction. For clarity of discussion I just describe outgoing journeys in this post as return journeys are exactly the same from a map point of view.