*As part of the [Grassroots Mapping Curriculum](/wiki/mapping-curriculum) series.* ##

Creating a map from a set of aerial photos## MapKnitter is a free and open source tool for combining and positioning images (often from [MapMill.org](http://mapmill.org)) in geographic space into a composite image map. Known as “orthorectification” or “georectification” to geographers, this step covers the process of figuring out where images can be placed on an existing map, and how they can be combined, or “stitched” together. You are likely to have many images of overlapping or identical areas, which is why MapMill or some type of sorting is used to determine which source images to use from the original set. 

The manual process differs greatly from automation in this type of map making involves a cartographer making decisions and crafting the maps using their individual judgement and style. But the approaches are similar in that they use some type of additional information (usually pre-existing imagery of a lower resolution) as a reference, and that they are bound to specific cartographic elements such as map scale and map projection.
 ##Tutorials## Learn more about MapKnitter, including advanced techniques, in this list of tutorials: * [Introduction to MapKnitter](https://www.youtube.com/watch?v=NOikqxIIFBc) - Learn to turn aerial images into maps with the Public laboratory's open source MapKnitter.org tool. Upload an image, rotate, distort and stretch it onto a reference map, and use the transparency and outline modes to check how close the fit is. Then export to GeoTiff or OpenLayers/TMS. ###Upcoming tutorials### * Photoshop tutorials: * Choosing a resolution * Importing a base layer from google maps or another source * Warping a difficult image with the mesh "warp" tool * Turning a Photoshop-produced map into a GeoTiff using MapKnitter