Pitney Bowes MapInfo Professional - Manual (Page 220)

When you merge the layers from the source map on top of the destination map, the destination map
settings take precedence. This means that the clip regions and coordinate systems, for example, are
based on the settings in the destination map. If the destination map does not allow raster reprojection
and the source map has a raster layer, the coordinate system of destination map could change.
Consider this example of a vector map and a raster map. Many times you want to add detail to a map
by merging it with another open map. You can think of the map you are dragging or copying layers from
as the source map.
Figure: Alaska Raster Map (Source Map)
You can think of the map that you are dragging or copying the layers to as the destination map.
Figure: Alaska Vector Map (Destination Map)
MapInfo Professional does not copy the Cosmetic layer objects or thematic layers from a source
map to the new window, so any symbols or features you have created there do not merge. Note:
MapInfo Professional 12.5 220
Working with Text on the Map