Geographic Information Systems

Geographic Information Systems (GIS) bring geographic measurements together with powerful tools for visualization, analysis and modeling. These technologies are being integrated into our planning and decision-making processes.

In accordance with the National Environmental Policy Act (NEPA) process, environmental documents are prepared that state:

• the purpose and need of a TxDOT transportation project,
• any existing environmental and socioeconomic conditions,
• environmental consequences of the project, and
• alternatives to the proposed alignment of the project.

The following GIS maps show environmental elements that are considered in Texas highway construction projects.

• Air Quality
• Edwards Aquifer Contributing Zones
• Vegetation Types

The amount of data needed to make sound environmental decisions during the NEPA process, like that contained in the GIS maps above, could cause an overload of information. To assist in the NEPA process, Region 6 EPA developed an assessment tool to systematically consider single and cumulative environmental impacts. The Region 6 EPA GIS Screening Tool (GISST) is designed to facilitate a better understanding of environmental effects and allow the EPA to share technical and regulatory data with industry, the public and other stakeholders.

This tool uses a mathematical formula to provide a weighted environmental score to a GIS spatial grid indicating environmental concerns in a project area. The 1K grid data can be symbolized on a map with a score of one (low impact) to five (high impact) or Present/Not Present. The score is based on EPA-developed criteria for census data, impaired streams, threatened and endangered species data, flood data, national land cover data, aquifers, watersheds, roads, ozone level, toxic release inventory data, soil data, hydrology units and environmental facts.