I've used both World2XPlane and Ortho44XP to generate overlays, but I can't really tell which is best (I guess the best proof would be how well they follow the orthophotos.}

I'd like to use the freeware package to make the roads transparent, but I first want to use the most accurate overlay.

Any thoughts on the subject?

 

John in Indiana.

Ortho4XP doesn't generate overlays, it simply extracts them from the default scenery (or HD Mesh v4), so all it's doing is placing the default scenery objects on top of the orthoimagery. As for accuracy, well it's autogen based on low resolution land-usage data, so whilst it looks believable, it is obvious that it isn't accurate when comparing with the ortho imagery. The biggest problem I found with this approach wasn't the autogen, but rather the tree placement that can look quite messy.

World2XPlane scenery on the other hand will use OpenStreetMap data to place buildings and forests (and optionally fallback to the default scenery where there is no data), so it's more accurate where data is available. However, the buildings don't look as nice unless you're using a ready-made W2XP scenery such as xEurope which has custom artwork for the buildings.