Of all the UK mapping sites I've seen, the most detailed are provided through Centro as part of their journey-mapping service. The maps give details of individual building footprints and property lines, which makes it very helpful in locating destinations and way points.
There are two ways of using these maps. One is through the journey planner at http://www.travelinemidlands.co.uk/cityplan. This is useful for planning bus trips, although it can be quite finicky in terms of wanting precise start and end points. The planner produces two kinds of map: a journey map of the route, and point maps of specific locations along the way. These maps show road routes only, so if one wants to walk or ride through a park, the map won't give you that information. Furthermore, it doesn't always give the most direct route.
For example, if you want to walk from Moseley Village to Moseley Bog, the journey planner suggests taking a bus to Kings Heath High Street, then another bus along Addison Road and Brook Lane to Yardley Wood road, instead of walking along St. Mary's Row to Oxford Road, and from there to Yardley Wood Road.
The second way to use these maps is to edit the URL to produce the desired information. This is even more finicky than using the journey planner, but it gives good results, as shown via the link below.
What I've done is find the X,Y coordinates for Moseley Crossing and Moseley Bog, then inserted them in place of the start and end points provided by the journey planner. I've also edited the start and end names. The one thing I haven't figured out is how to zoom at a particular level, but the page has zoom buttons that work in Internet Explorer (not Firefox). This produces a map with a more direct route along Oxford Road, and even gives the approximate distance of 1928 metres.
The most finicky part about this is finding the correct coordinates, and for this I've typically gone to Streetmap.co.uk and used their coordinate location and conversion utility, putting those numbers into the Centro URL and fine-tuning them until I get the precise location I want. So, by fiddling and fussing, one can come up with a nicely detailed map of a local journey. It doesn't work for all journeys, particularly short ones, such as from Moseley Crossing to Moseley Park and Pool entrances. But it's nice for the intermediate journeys.
Walk from Moseley Crossing to Moseley Bog