The Tellus Border project was a €4.8M EU INTERREG IVA-funded cross border project designed to map the environment and geology of the border region of Ireland. It was an extension of the successful Tellus project of Northern Ireland (http://www.bgs.ac.uk/gsni/tellus/). The project collected geochemistry and airborne geophysics datasets with the aim of merging the new and existing datasets into seamless cross-border baseline data. The airborne part of the project comprised the collection of low altitude magnetic, spectrometry and frequency domain electromagnetic data. The airborne survey was carried out by Sander Geophysics Ltd (SGL, 2012) between October 2011 and July 2012. Geophysical data measures variations in certain physical properties such as magnetic susceptibility, density, conductivity and content of radioactive elements. The data can be interpreted in terms of the distribution of rocks and soils and their structure. By using a combination of methods and in conjunction with other geological information such as existing mapping and drilling, conceptual models of the surface and subsurface can be developed. The new geophysical data allows existing geological maps and ideas to be tested and confirmed as well as highlighting new features and anomalies. This new seamless cross-border data set has allowed a detailed assessment of geological boundaries across the region. The main uses of this merged dataset are;