The Texas Gulf Coast Groundwater and Land Subsidence Program web application illustrates how groundwater, sediment compaction and land-elevation change are related in the Houston-Galveston region in Texas. The region represents one of the largest areas of land-surface elevation change, or subsidence, in the United States. Most of the land subsidence in this region has occurred as a direct result of groundwater withdrawals for municipal supply, commercial and industrial use and irrigation. The viewer shows how water levels have changed over time and how groundwater demands have affected land subsidence in the region with more than 40 years of groundwater and compaction observations. This long-term data is essential to the project, and was collected in cooperation with the Harris-Galveston Subsidence District, City of Houston, Fort Bend Subsidence District, the Lone Star Groundwater Conservation District and the Brazoria County Groundwater Conservation District.