georeferencer help
Fix Location of a MapGeoreferencer HomeGeoreferenced MapsGeoreferencer Compare
Georeferencing historical maps enables new understandings of the maps by comparing them to modern maps through visualization and analysis. It also creates the ability to search old maps for locations and to compare old maps to each other. Use the Georeferencer tool to place location points on the old and new reference maps. This can take some time but the results are very satisfying both to the user and as a contribution to our online library - other users will be able to make use of all georeferenced maps. Once maps have been georeferenced, they can be found through the LUNA viewer or at the Georeferenced Maps page. The various pages for the process have ? buttons to provide detailed help as needed.
The steps of georeferencing are as follows:
1. Choose a map to georeference, either with the Random Map button or the Search LUNA... button.
2. The map will open on the right side window with a modern map in the left side window. For more information about the map, click on the This Map tab.
3. You have several choices of modern maps to use, click on the upper left Globe symbol menu to choose the best one for the area in question.
4. If the historic map location is not clear, find the name of a town or street and search on that term in the modern map search window.
5. Use the zoom in + or out - button to navigate the maps, or the scroll wheel on your mouse.
6. Find common locations on the old and modern maps and place sets of points on each. Three points are the minimum required, but more than three points will increase accuracy. Use the Coordinates tab to detect errors.
7. Spread the points as evenly as you can across the maps for better results. Try to extend points to the map margins. If you make a mistake with any point, mouse over a point and hit delete, then re-position the point and click on the map until the points number shows.
8. When you are finished placing points, use the Clip tool to crop the map just inside the map border. This will make the map blend more easily at the edges with the modern map and also define the area of the map's coverage in our database. Then click on the orange Save button and the map can be viewed in the This Map window and the Georeferencer Compare window. If you have not logged in you will be asked to - setting up an account is free.
9. You can view the historic map in 2D or in 3D or using the Side-by-side viewer in the Georeferencer Compare window. Maps that show mountains and other elevated areas will use the built in DEMs (Digital Elevation Models) in the 3D viewer to show those areas in three dimensions.
10. In the Overlay & Compare page (Georeferencer Compare) you can view one map or search for maps from various sources, and then compare them using several different views - Overlay, Grid, Swipe, and Spy glass.
11. If the map needs correction or refinement of points, sign in and click on the Georeference tab in the This Map window and you can add or correct points. To get to the Georeference tab if you are in the Georeferencer Compare view, just click on the name of the map in the upper right box. Use the Coordinates tab to identify inaccurate points. Remember that very old maps may have inaccuracies in the original cartography and understanding the degree of these inaccuracies is one of the things that Georeferencer makes possible.
12. Polynomial and TPS views of the map use more complicated calculations to render the map and may result in more accurate renderings, but they will require more points to be made and they may distort the shape of the map. The default view is Affine, which will stretch the map but not alter its shape.
13. The Cutline (the box made with the Clip tool in the Georeference tab) may be turned on and off by checking and unchecking the box next to the Cutline label in the Cutline tab view.
14. From the This Map pages, use the GeoEditor to locate and measure areas, distances, locations, and more. Use the Transcribe feature to annotate the maps.
15. Advanced users will be able to export the georeferenced map using the Use in GIS apps - Get Link in the lower left of the This Map view. This will enable viewing the maps in various GIS web based and desktop programs.
16. If you find bugs or problems, use the Hamburger drop down menu in the upper left corner of all screens to send us a message about the problem with the Send Feedback tab.
17. Klokan Technologies developed Georeferencer with the Moravian Library. You can combine and compare maps found at the Georeferencer pages at the National Library of Scotland and the British Library, along with maps from our collection in Georeferencer, as well as all the maps in Old Maps Online.