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OS MasterMap Managed GB sets frequently asked questions
How do I avoid a gap between my data holding and the first MGBS delivery?
Subscribers have two options if they wish to avoid the temporal gap between their existing data holding and the first delivery from the Managed GB sets (MGBS) service: they can either take a change-only update (COU) order with their first delivery or they can take full resupply. If the customer wishes to take a COU order then they need to provide the 'since date'.
Why are the chunk sizes different for MGBS OS MasterMap® layers?
OS MasterMap Managed GB sets (MGBS) are available in either 25 km x 25 km geographical chunks or 30mb non geographical chunks for all layers except for OS MasterMap Topography Layer which is available in 5 km x 5 km geographical chunks or 30mb non geographical chunks. This is for efficiency, both for you and for Ordnance Survey. Topography files are relatively large, and so 25 km x 25 km chunks would be too much information for each file, especially in urban areas.
It is possible for Ordnance Survey to extract 5 km x 5 km chunks for the other layers, but it would create around 25 times as many files to load, which would be disadvantageous to most.
What is a chunk and can I order different chunk sizes for different layers?
Chunking is a way of breaking OS MasterMap orders into manageable parts through the creation of a series of subsets of data or ‘chunks’. The drop-down list for the chunk size options will show you what chunk sizes are available for your OS MasterMap® contract and order options.
There are two types that can be ordered:
Geographic chunking
This breaks the data into chunks determined by a geographic extent selected by the customer.
Currently the size of geographic chunks available are:
2km by 2km, 5km by 5km and 10km by 10km.
We will also supply 25km x 25km chunks for some Managed GB Sets (MGBS) of data.
Geographic chunks are not hard clipped and complete OS MasterMap features will be supplied that will cross the actual geographic area.
Because of this, you will have duplicated features that will appear in each adjoining Geographically chunked file.
The chunks that apply to your order do not come from a pre-defined grid as was previously used for our Large Scale data supply.
The chunks are unique to each order area.
Non-Geographic chunking
Data is supplied based on the size of files selected and not a fixed geographic area.
Currently the available file sizes are 10mb, 30mb or 50mb.
Data provided in non-geographic chunks should not contain any duplicate features.
Geographic or non-geographic chunking and the corresponding area or size option is specified by the customer at the point of ordering.
All OS MasterMap data is supplied in a compressed .gz files.
Does the Managed GB sets service cost extra?
No, it is simply another order and delivery option to current OS MasterMap® customers on the current service.
Will my organisation require any additional software to use the MGBS service?
No extra software or hardware should be required to use the Managed GB sets (MGBS) service. You can use the same software and hardware as you currently use with the normal service.
How will orders delivered by the MGBS method differ from other orders?
Using the standard service, if an order is created for more than one layer (from OS MasterMap® Topography, Address and Integrated Transport NetworkTM (ITN) Layers) then each chunk, or file, will contain multiple layers. Likewise, if an order is created for both ITN themes, then each chunk will contain both themes under the current supply system.
If the same orders are taken within the Managed GB sets (MGBS) service, each chunk will contain only one layer, or if it is OS MasterMap ITN Layer, then only one theme.
Managed GB sets orders will be sent on CD or DVD, but not via FTP.
When will I recieve my MGBS?
Customers will now recieve their MGBS update earlier in the cycle, as orders will be direct copies from a single master dataset, rather than bespoke orders with individual customer names and order numbers.
The speed of MGBS order fulfilment may still vary with demand for data through our publication systems. Typically the master discs will be created 10-15 working days after the publication date, then copied and despatched to customers. Therfore we are unable to give specific dates when MGBS orders will be ready.