Watershed Education - Historical Aerial Photographs
The following photographs are referenced to the school so that middle and high school students can investigate land-use change over time for the area surrounding their school. They were created to support the Project Learning Tree module, Exploring Environmental Issues in the Places We Live.
To save images, right click link and select "Save Target As"
Instructions for using dot grids
A transparency with random dot grids can be used to calculate the percent area for different land uses on an aerial photograph. For example if you have a 100-dot grid, and 33 of the dots fall on forest land, then 33% of the area on the photograph is forestland.
Place a dot grid over a map. Make sure that all the dots on the grid are over the map area. Secure the transparency to the map so that it does not move while you count your dots. What might be the advantage(s) of using a random dot grid over a dot matrix grid? What might be a disadvantage?
- Random dot grid #1 to approximate area of landuse change
- Random dot grid #2 to approximate area of landuse change
- Dot matrix grid (2 dots per inch) to approximate area of landuse change
Count the number of dots that fall over every land use you are interested in calculating.
