I'm guessing that you are looking at a map of Beleriand? Well, on the far right you should see the Ered Luin (Blue Mountains). That is in the far northwestern corner of your LotR map. I don't want to give too much away, but the coastline isn't completely similar because the much of the region (Beleriand) where many of the events in the Sil take place is not there in the third age.
I think Kransha and I have different copies...mine only has one map, a map of Beleriand. I have a DelRey copy. If you only have one map it is probably a map of Beleriand, which would have parts corresponding to your LotR map. If you have more (?) then I wouldn't know.
I hope this makes sense.