View MasterMap Change-Only Updates (Part 1)

GGP 2009 introduced the ability to create overlays that read and write data stored in geospatial databases: Oracle Locator, SQL Server 2008, PostGIS. We can use this feature to register a layer that will show the MasterMap change-only updates on a map.

To prepare for this demonstration, I have loaded a MasterMap database with an initial load received in December 2009. I subsequently applied the following five COUs:

• From 15/12/2009 to 02/02/2010
• From 02/02/2010 to 16/03/2010
• From 16/03/2010 to 27/04/2010
• From 27/04/2010 to 08/06/2010
• From 08/06/2010 to 20/07/2010

GGP 2009 allows creating overlays that read data from database views in addition to ordinary tables. I took advantage of this, creating a view called VEW_COU_TOPOGRAPHICAREA, which will return only records updated after 15 December 2009 by Ordnance Survey:

SELECT
FID, FEATURECODE, VERSION, VERSIONDATE, THEME, CALCULATEDAREAVALUE,
CHANGEDATE, REASONFORCHANGE, DESCRIPTIVEGROUP, DESCRIPTIVETERM,
MAKE, PHYSICALLEVEL, PHYSICALPRESENCE, POLYGON, LOADDATE, MI_PRINX
FROM
TOPOGRAPHICAREA
WHERE
VERSIONDATE >= '2009-12-15 00:00:00'

Using the ATFEdit Setup application, I create an Area overlay labelled “MasterMap Area COU”, which will obtain data from the VEW_COU_TOPOGRAPHICAREA view. Since I am connecting to a SQL Server 2008 database, the layer will be created with the advanced parameter SafeSpatialQueryMode set to “true”. For a large dataset such as MasterMap Topography, this is going to have a significant impact on performance. Since MasterMap is almost guaranteed to be free from invalid geometries that might be hard to handle for SQL Server 2008, I can change the SafeSpatialQueryMode to “false”.

We can now add the new overlay to a script, and show the change-only updates on a map:

(Part 2 of this post available here)

Read more: MasterMap, OrdnanceSurvey