Change-Only Update (COU) Supply

The OS MasterMap Highways Network – Paths can be ordered as either Full Supply or Change-Only Update (COU). The GeoPackage and vector tiles files are full GB coverage so are not available as a COU. The GML structures for Full Supply and COU are different. The differences are fundamentally the open and closing tags which will have an impact on how you choose to load the product. Examples of the different opening and closing tags can be found in GML examples. If a customer wishes to move their order from Full Supply to COU then they will need to receive an initial supply and apply the COU file to an initial supply. The COU should not be applied to a Full Supply order.

Full Supply

When an order for Full Supply is placed, the product will contain all features for the customer’s area of interest. When a product refresh is ordered, for this type of order, the supply will contain all the features for the area of interest which will include features that have not changed. This supply mechanism will not explicitly identify which features are new, have been modified or have been removed. This can still be identified by querying the reasonForChange and the beginLifespanVersion attribute.

Change-Only Update supply

When an order is placed for COU, the first order received will be an initial supply. Initial supply refers to the first order that a customer takes of OS MasterMap Highways Network under the COU order type. An initial supply contains all features for the complete area covered by the order, and every feature will be an “insert”. Updates, which contain the latest changes to the features are sent out automatically.

Following the initial order, a COU will be supplied, at the selected update schedule of the customer. COU only contains new features, new versions of features and information about deleted features. A feature can be deleted from the customer’s holdings for two reasons; the feature has been deleted and the id will no longer exist in the product, or the feature has moved outside of the customer’s area of interest but still exists in the national product and therefore could be reinstated in a customer’s holdings. To identify the difference between the two deletes the reasonForChange can be used. If the value is “end of life” then this feature has been permanently deleted whilst any other change value would indicate the feature has moved outside of the holdings and could be reinstated in future. Any feature within the area of interest that has not undergone any change will not be supplied.

The features within the initial supply and COU are provided as transactions. A transaction identifies if the feature is new, modified or removed from the product. The three types of transactions are:

1. <os:insert>

These are features which have been newly inserted into the product or the customer’s area of interest since the last product supply.

1. <os:replace>

These are features which have had either a geometry change or an attribute change since the last product supply. The whole feature will be supplied, not just the changed attributes. The recommended action would be to completely replace the feature which currently exists in the customer’s holdings.

1. <os:delete>

These are features which have ceased to exist in the last product release or have moved out of the

customer’s area of interest. Features which have been deleted will be supplied with the entire feature’s attribution. These features should be removed from the customer’s live data holding.

The initial supply will contain an insert transaction for all features in the customer’s holdings. The following COU supplies will have insert and replace transactions in one GML file and deleted features will be supplied in a separate file. Where a delete file has been supplied, this must be loaded before the file containing inserted and replaced features. There are examples of the different types of transactions in GML examples.