Article source: ShareMap.org
ShareMap is slowly phasing out from beta stage. Feature set is almost complete and dozens of maps created with ShareMap enriches multiple Wikipedia articles.
There are two major features introduced recently:
OpenStreetMaps is enormous source for geospatial data. Implantation of import mechanism from OSM was one of first features of ShareMap. But sometimes OSM data is not enough, especially when we try to create historical map. For example if we want to create map of dismantled tramway system in Cleveland we cannot find information about track position at OSM. But we can reuse pre war map of system (with expired copyrights, so it is 100% comply with Creative Commons license). We can treat this old map as overlay to our interactive map, but first of all we have to calibrate it. In simple words calibration is just selecting of several calibration points on raster map (old one) and interactive map. After point selection system warps. Under the hood well known open source GDAL library is used. In this video map calibration process is described in detail: