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.

2 comments

  1. Dave Smith

    Have you examined the approach that ArcWeb AddressFinder takes? Aside from that example, there are a number of ways that a geocoder backend system can be architected to present the results, but ultimately with the ideal solution being an approach similar to the one you describe or ArcWeb, where the results are presented as a list, with confidence scores.

    If the resultset is greater than 1, then the frontend code must know to step through the list further and present the options as alternatives for the user to select from…

  2. Piergiorgio

    Ed, interesting issue.
    What if the BoundingBox of the Product”B” overlays Swindon but the “real” features don’t?
    Example: the Product”B” is a dataset of discrete linear features (rivers), and none of them really intersect Swindon!!
    Are my results still correct?

    Pg

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