When georeferencing a historic scanned map, what must be done if it is in a different projection than the current spatial data?

When georeferencing a historic scanned map, if it is in a different projection than the current spatial data, the correct action is to georeference the image again. Georeferencing involves aligning the scanned map with the current spatial data by transforming the coordinates of the scanned image to correspond to the coordinate system of the existing data layers.

Different projections can distort the representation of geographic features. Therefore, it’s essential to ensure that the coordinate system of the historic map matches that of the current data to ensure accurate spatial analysis, overlaying, or analysis of spatial relationships. This process typically involves identifying common reference points or control points on both the historic map and the current spatial data and adjusting the scanned map accordingly.

The other options do not address the need to ensure that the projections align. Ignoring the projection would lead to inaccuracies in spatial analysis. Simply converting it to a raster layer does not rectify the issue of differing projections, and using it as a basemap without the correct georeferencing would compromise its utility in analyzing current spatial data effectively.