oooh this is my subject, although i can not tell you of the map of arda in the third age only in the first, but what Grondy said is true. Recently ive been searching for various books on the maps of ME or anything Tolkien related, and low and behold, i found an amazing book that had big posters of all the main maps of Tolkien's complicated world.
They are beautifully drawn by John Howe, i have studied them very carefully, i have gained much knowledge from them, especially the map of Beleriand, my favourite of them all. They are all drawn ot the time period of the book that they are based on, ME is at the end of the third age. Beleriand is the time of the Silmarillion, there is even a map of Rhovanion (Mirkwood Forest) at the time of Bilbo Baggins's journey to The Lonely Mountain and there are loads more. I suppose you can call the maps 'my subject' so to speak. Which i am glad i have found.
Does anyone else have any specialised books on the maps??? id be very glad to know which ones you have and then find for myself