CPRE Gloucestershire has been awarded £16,500 from the National Lottery Community Fund to launch a new project called LandWise.
The project has also received £2,576 from The Summerfield Charitable Trust.
LandWise will use volunteers to identify overlooked brownfield sites across Gloucestershire and compile them into a county-wide database and digital map.
The charity says the evidence will be shared with local authorities to support sustainable planning decisions and encourage development on previously used land first.
CPRE Gloucestershire says the project aims to reduce pressure on greenfield sites and give communities a stronger voice in planning.
Director Louise Chandler-Mullins said LandWise will help local people turn their concern for the countryside into practical action.