I have a paper map that I am trying to digitize. I have scanned it and am trying to use ArcGIS to export the values and locations of the contour lines, but even before that, I have some trouble understanding the coordinate system used by this map.
On the map, it is stated that "Positions are referred to WGS84 datum" and immediately below that, "Projection: mercator". From my limited understanding of cartography, WGS84 is a geographic coordinate system (GCS), meaning that it is not a projection. So why is there a projection to this map?
Therefore, the next question is, which spatial reference system should I use for this map?