This is an invitation to use Mapjunction! A free web tool for map lovers and history enthusiasts. In Mapjunction you can compare any two maps from Boston and environ history. You'll see almost 400 maps and aerial photos that are the result of combining about 3000 individual maps and aerial scans. Just move the green wand from side to side to uncover history. Move the wand up and down to change opacity, and use the side bars to pick any map, aerial or atlas to explore.