About two and a half years ago Ordnance Survey released their OpenData. It keeps getting updated so anything that uses it can be updated and improved too. The Code-Point Open data which includes GB postcodes (not postcodes for Northern Ireland) were updated in August so I reloaded them on my postcode overlay. You can see more here, including my postcode finder.
Another one of the OS OpenData datasets that I particularly like is OS Locator. This gives a bounding box for each named road in Great Britain. If these names are compared to the names in OSM the anomalies can be derived and then a survey shows where the name or the whole road is missing from OSM or where the name in OSM or the OS Locator data differs from what is on the ground. ITO World publish the list of anomalies, grouped by local authority. The thing I like best is that as new OS Locator data is published, new anomalies appear, particularly where new developments are taking place. In effect OS are helping keep OSM up-to-date by pointing where new roads are being built. I use the map tiles ITO provide to show unresolved anomalies as an overlay on a comparison map to help track them down. We tracked down a couple of these anomalies and added more detail to OSM than the OS Locator data suggests because the developments have moved on since OS added to their dataset.
In north Hull, around Kingswood, there is a a substantial development steadily being built. It keeps getting highlighted on OS Locator data as it gently expands. It is going slowly, probably because money is tight, but nonetheless it is gradually filling up the allocated space. Ground level of the development is below the level of the high embankments that retain the nearby meandering river Hull. The nearest higher ground reaches to a 10m contour about two kilometres away. Older maps show the former criss-cross pattern of drainage ditches leading to Engine drain and Wawne drain. Water from these drains has to be lifted by pumps (hence the name Engine drain) into the river Hull which wriggles its way through the city to the tidal Humber about five kilometres away. Some of the former farmland that this development is built on belonged to Ings farm and surrounds a very small woodland called Ings plantation. Ings is a local word meaning a water meadow or flooded meadow. Some of the trees in the plantation are alder, which grow in wet places, such as marshes or seasonally flooded areas. All this points to why no one built here before - flooding.
I'll add the development to OSM as it grows, but I wonder if it is also being added to maps in insurance companies as an area liable to flood.