The survey data combines data from a number of different surveys into one merged dataset. The individual surveys consist of; (1) Tellus Northern Ireland, 2005-2006 (2) Cavan-Monaghan, 2006 (3) Tellus Border, 2011-2012 (4) Tellus North Midlands, 2014-2015 (5) Block A1, 2015 (6) Block A2, 2016 (7) Waterford, 2016 (8) Block A3, 2017 (9) Block A4, 2017 (10) Block A5, 2018-2019 (11) Block A6, 2018-2019 (12) Block A7, 2019 Combined a total of 382,567 km of data were collected over a total area of approximately 70,438 km2. The plane flew along survey lines 200m apart at a height of about 60m. The system measures the Earth’s Magnetic Field and how it changes due to different types of rock. This data shows the magnetic gradient (changes in the magnetic field). The magnetic gradient allows us to map different types of rock close to the surface. This is a raster dataset. Raster data stores information in a cell-based manner and consists of a matrix of cells (or pixels) organized into rows and columns. The format of the raster is an image (TIFF). The image cell size is 50m which means that each cell (pixel) represents an area on the ground that is 50 meters across. The image also contains location information (GEOTIFF). Each cell has a different colour representing the magnetic gradient of the rocks: black for low, grey for medium and white for high. The Tellus survey is a national airborne geophysical and ground geochemical mapping project managed by the Geological Survey Ireland.