Forest map

This map of Billerica, Massachusetts is one of the earliest known examples of the use of data overlays as an analytical technique. In 1912, as part of a project for the town of Billerica, landscape architect Warren H. Manning worked with residents to analyze how the forest had changed over the last 60 years. Here, the vibrant red-shaded areas represent “wooded lands” in 1853, while the areas of diagonal hatched gray lines represent wooded lands in 1912 (the unshaded white areas are “in cultivation, pasture, and grass”). By overlaying these data layers and measuring the differences in acreage between them, Manning’s map documents where forest overtook farmland between 1853 and 1912.