There are many competing requirements for the use of land in the densely populated British Isles. Options are constrained by existing development, economics, the need to safeguard the environment and to reclaim damaged land, and the pressure for urban renewal. Land use planners attempt to balance the various issues and requirements and to identify the best possible solution. Geology, geotechnics, geomorphology, hydrogeology and related sciences can provide essential information on additional constraints to development (such as land instability, poor foundation conditions, active erosion and deposition, likelihood of land or water contamination, flooding and seismicity) and resources for development (including mineral and water resources, usable underground space and good foundation conditions). Recognition of these factors permits safer, more cost-effective planning and development and allows rational decisions to be taken on the exploitation or sterilization of the Earth's resources. However, few planners and administrators have any training in these relevant sciences. Thematic geology mapping provides an important means of communicating facts and interpretations to planners but only if the results are presented in ways which can be readily understood and appreciated by non-specialists. The communication gap can only be bridged if earth scientists and planners cooperate in designing methods of map presentation.