MapWarper is a free, open source tool used to georectify maps, which means to connect a historical map image to contemporary GIS coordinates. Once you match points on the map with their corresponding coordinates, the tool will “warp” the image to fit over the contemporary map. Then, you will be able to map and gather spatial data directly onto the georectified image. This can be a powerful tool to understand the spatial orientation of past places or events and to present spatial history projects directly onto contemporary maps. It can also be a great way to discuss the history of maps with your students, and different historical approaches to visualizing space.
How to Use
MapWarper may seem a bit foreign at first, but the interface is relatively easy to use through a few steps which are basically: upload or select a historical map, rectify or select control points common to the historical and contemporary maps, warp the historical map into a rectified layer, and export your map for use. There are many useful guides online to help you that go into more depth than this tutorial. For example, see the following Map Warper tutorials at Doing Digital History and GitHub.
1. To use MapWarper, you first need to create a free account.
2. Once you’ve logged in, you’ll need to get the historical map you’d like to use into MapWarper. Do this by selecting the “Upload Map” tab at the top of the page. Once here, fill in the identifying metadata for your map and then upload the file either through a file upload from your computer or through an image URL. The map image you upload should be the highest resolution possible to avoid pixelation in the warping stage. Alternatively, or if you simply want to try out MapWarper, you can browse through already-uploaded maps in the “Browse All Maps” tab.
3. Once uploaded, you are ready to rectify your map. To do this, open the map you plan to use and click on the “Rectify” tab at the top of the page. This page will display your historical map and a contemporary map side by side. Make sure both maps display roughly the same area using the zoom and “hand” tools. Once the display is where you’d like it, select the “point” icon at the top right corner of each map. Choose a point clearly visible on each map and place a point there. Then, click “Add Control Point” and the point and its coordinates will appear below. You should repeat this step at least three times, and try to focus on points across the map rather than condensed in one area.
4. Once you have selected three or more points on the maps, click “Warp Image!” to create your warped map. You can view your map under the “Preview Map” tab. Here, you can make sure the map has warped properly and you can adjust the transparency between the two. If you need to make changes, refine your points using the instructions in step two. Once you are satisfied, you are ready to export your map.
5. To export your map, select the “Export” tab at the top of the page. Here, you will find a number of export options to suit a variety of needs. If you are unsure what file you will need, the “Next Steps” section of this guide provides a breakdown of how you can use each type
MapWarper can be used in the classroom in a variety of ways. Georectifying a map allows you to gather coordinate data about historical sites or locations. For example, have students use MapWarper on a historical map of a city you are studying, and then have them find the contemporary coordinate data for different sites on the map. This allows students to collect spatial data that can help to understand changes and consistencies in the landscapes of cities over time. Another use would be to tell a spatial story using your rectified historic map as a layer so that the points appear on this map rather than on a contemporary GIS map like Google Maps or Open Street Maps. For example, you can use the Tiles export option to upload a rectified map as a layer into a spatial storytelling tool like StoryMapJS.