The next release of Change-only Update data for OS MasterMap will be put into service on Tuesday 24 March 2009. The currency date of the new data will be 20 January 2009.*
Change-only Update (CoU) applies only to the OS MasterMap data. It does not apply to any other data product.
EDINA collates all the data changes released by Ordnance Survey over a 6-month period, and makes these available through Digimap approximately every 6 months. The previous update was released in September 2008.
What is the point of Change-only Update?
Change-only Updates enable you to update your data holding without needing to store multiple copies or versions of the same data. By taking only the changes to the data you hold you can minimise the storage requirements for your data, while still maintaining an up-to-date dataset. This is particularly useful if you are studying changes to an area over time.
Most users will not need Change-only Update. CoU is only useful to you if you already have a full copy of the original data to which you can apply the changes.
How do I download CoU?
You can download Change-only Updates only for data orders you have already submitted within Digimap’s Mastermap Download facility. Go to the Your Account page within Mastermap Download and scroll down to the table of Orders.
You will see a list of all your previous Orders, and in the final column you will see whether or not CoU is available for that Order.
If CoU is available, click the radio button in the far left column for the Order you require. Below this table, you will see two buttons in a blue box:
Click the first button to Order Change-only Update. The data file will be delivered in the usual way: you will receive one email to say your Order has been received and is being processed, and a second email to say your data is ready for collection.
If you submit a new order for OS MasterMap data, by defining the Layer, Themes and your chosen area, you will automatically receive the latest version of the data; this will include all the latest changes. Change-only Update will therefore not be available for such an Order until the next batch of CoU is released.
You submit an Order for data on 20 March 2009. In the Orders table under Your Account, the Order details say that CoU is not available. This is because you already have the latest version of the data.
If you submit a second Order for data on 27 March 2009, you will also see that the order details say that CoU is not available. Again, you have the latest version of the data; it includes the changes which were released on 24 March.
If you go back to look at your first Order (submitted on 20 March) on 2 April 2009, you will see that COU is now vailable for this Order. This is because the changes released on 24 March are now available; they were not available when you submitted the original order.
* Although the latest update is dated 20 January 2009, it takes time for Ordnance Survey to process and release these data, to send them out to EDINA and for EDINA to process and load the data into the database. This accounts for the time delay between the “freeze date” of the database (20 January 2009) and the release date (24 March 2009).