# Release Notes {% hint style="info" %} ## Known data issues and service disruptions Any interruptions or data issues impacting the OS MasterMap Topography Layer product will be documented on the [Known Data Issues and Service Disruptions page](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/os-mastermap-topography-layer-known-data-issues-and-service-disruptions.md). {% endhint %} ### [OS MasterMap Topography Layer – May 2026 Release Note](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/release-notes/may-2026.md) This release note provides information about the May 2026 release of OS MasterMap (OSMM) Topography Layer. ### [OS MasterMap Topography Layer – March 2026 Release Note](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/release-notes/march-2026.md) This release note provides information about the March 2026 release of OS MasterMap (OSMM) Topography Layer. ### [OS MasterMap Topography Layer – February 2026 Release Note](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/release-notes/february-2026.md) This release note provides information about the February 2026 release of OS MasterMap (OSMM) Topography Layer. ### [OS MasterMap Topography Layer – January 2026 Release Note](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/release-notes/january-2026.md) This release note provides information about the January 2026 release of OS MasterMap (OSMM) Topography Layer. ### [OS MasterMap Topography Layer – November 2025 Release Note](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/release-notes/osmm-topography-layer-release-note-template-month-yyyy-1-1.md) This release note provides information about the November 2025 release of OS MasterMap (OSMM) Topography Layer. ### [OS MasterMap Topography Layer – October 2025 Release Note](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/release-notes/october-2025.md) This release note provides information about the October 2025 release of OS MasterMap (OSMM) Topography Layer. ### [OS MasterMap Topography Layer – September 2025 Release Note](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/release-notes/september-2025.md) This release note provides information about the September 2025 release of OS MasterMap (OSMM) Topography Layer. ### [OS MasterMap Topography Layer – July 2025 Release Note](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/release-notes/july-2025.md) This release note provides information about the July 2025 release of OS MasterMap (OSMM) Topography Layer. ### [OS MasterMap Topography Layer – June 2025 Release Note](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/release-notes/june-2025.md) This release note provides information about the June 2025 release of OS MasterMap (OSMM) Topography Layer. ## Feature validation datasets for GML orders A feature validation dataset (FVDS) is a set of files that can optionally be supplied with either a Full Supply Change-Only Update (COU) or an Area of Interest (AOI) COU of an OS MasterMap Topography Layer order in Geography Markup Language (GML) format. It's divided into files on a non-geographic basis, using a 10MB nominal file size. The comma-separated value (.csv) text file format of the FVDS gives the TOID, version number and version date of every feature that should exist in the current data holding, based on the polygon extent, themes, polygon format and extraction date of the current order. Each .csv file is compressed to a .gz file using the same compression algorithm used for the OS MasterMap Topography Layer GML files. {% hint style="success" %} ## You can: * Order an FVDS for your Full Supply COU or AOI COU orders of OS MasterMap Topography Layer in GML format. * Use the FVDS to validate that your OS MasterMap Topography Layer data holding contains the correct set of features after loading; it reports on all the data it expects to find in the holding after the application of the supply, not just what is contained in the supply. * Use the FVDS to conduct periodic checks on data holdings maintained by a COU regime. * Use the FVDS with both geographic and non-geographic chunk file options (see the [GML supply options page](/os-downloads/products/maps-and-imagery-portfolio/os-mastermap-topography-layer/os-mastermap-topography-layer-overview/product-supply/gml-supply-options.md) for more information about chunking). {% endhint %} {% hint style="danger" %} ## You can't: * Order a FVDS for GeoPackage or vector tiles (MBTiles) format orders of the product. * Order a FVDS for a non-COU Full Supply order of OS MasterMap Topography Layer in GML format. {% endhint %} --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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