Map Search.. How difficult can that be ?

Well actually, more complex than you might at first think… If you have bought a map online from Ordnance Survey in the past couple of weeks you will have used a redesigned store application that features a geographic search capability which recommends mapping products based on location.

mapsearch

This is actually a more difficult process than you might imagine, the search works across a range of OS and Partner products each of which are at different scales and which have different extents e.g they cover different areas, which often overlap.

There are two ways to search, one driven using a webmap (a simple ArcIMS WMS implementation) that provides a point to base the geographic search on, and a more sophisticated gazetteer search.

The gazetteer search is exciting in that is uses not just a list of placenames and points, but also place names and areas where appropriate classified by settlement and feature type.

For example enter “swindon’ into the search, and the system would retrieve ..

  • Swindon (Urban Region) – The area of the town
  • Swindon (Unitary Authority) – The larger area of the unitary authority
  • Swindon Swindon (Town) – A single point representing the centre of the town

As well as the villages Swindon in Gloucestershire, Staffordhire and the hamlets of Swindon in Northumberland and the Scottish Borders classified as such.

The user is then able to select the ‘Swindon” that is right for them, and then the really clever stuff happens..

A query is made to a Oracle Spatial database, overlaying either the point or polygon onto polygon extents of all the potential porducts and where there is an overlay geographically the products are selected.

Mapsearch how it works

The selected products are then ordered by the amount of coincidence between the area of search and the extent of the product, and these are then returned to the user. So in the example above product B would come before Product A as there is greater coincidence. ( yes I know the diagram looks bad in Internet Explorer – it’s a bug – use Firefox !!)

Like many innovations to the user this seems “no big deal”, but now you know different!! and we are actually using geographic information in a real business process , a case of actually doing as we say..

Written and submitted from the Holiday Inn Express Hotel, Poole, using my Vodafone 3G network card.

5,000 changes a day and other urban myths..

We all know the statistic that 80% of all information is spatial, but I guess like most people I’m not clear where that particular figure has come from, and thinking about it.. I not convinced it is actually true. There is much information held in databases around the world which is about activities which happen at specific locations, but as much as 80% ?

Another much repeated statistic is that Ordnance Survey makes 5000 changes to the national geospatial database every day – this time however, although I’m not sure where the statistic came from, I can put more accurate figures in place.

As part of the development of a new Oracle Spatial database system, we have looked at the number of transactions going through the database in order to scale the system, a 10 node RAC cluster by the way ..

In general day to day operations the OS actually makes between 30-50,000 changes per day, representing the modification of existing features in the database and the addition of new features into the landscape, things like new housing estates.

Over the past few years however a larger than average amount of change has been happening as a result of the Positional Accuracy Improvement Programme, resulting in peaks of 500,000 changes in a day !!

These figures sound a lot especially compared to the often stated 5,000 changes a day, but you need to remember the database contains around a billion individual features.

We really did need a new database !!!

Written and submitted from home, using my home 802.11 network.