The purpose of this chapter is to record the sources of data (with examples based on Irish resources) that can help a researcher's work. Its major beneficiaries are expected to be those who assemble Geographical Information Systems and those involved in the modelling process. A selection of topics has been chosen to show the range of information that is available and where shortcomings exist. Map data acquisition and storage, modern developments in spatial representation and the use of such data in land resource appraisal are introduced. Groundwater, surface water, marine resources, soil and vegetation resources are assessed. The discussion of land information and appraisal shows how data from a wide variety of sources, collected by personnel from disparate institutions and for widely differing purposes, can be assembled, reprocessed and interpreted for a range of uses - uses, perhaps, that the original surveyors never even dreamed of!