A Digital Terrain Model (DTM) is a digital file consisting of a grid of regularly spaced points of known height which, when used with other digital data such as maps or orthophotographs, can provide a 3D image of the land surface. This download contains OSNI 10k sheet numbers 1-50. This is a large dataset and will take sometime to download. Please be patient. This service is published for OpenData. By download or use of this dataset you agree to abide by the LPS Open Government Data Licence. Please Note for Open Data NI Users: Esri Rest API is not Broken, it will not open on its own in a Web Browser but can be copied and used in Desktop and Webmaps