Hello Gothmog. The geography of the North is a bit tricky! For example, on Tolkien's second Silmarillion map the distance between Menegroth and Thangorodrim is 218.75 miles (just under 73 leagues). Yet in The Grey Annals (written by JRRT in the 1950s) however, we have a distance of 150 leagues (450 miles) from Angband's gate to Menegroth. Christopher Tolkien notes that this... 

'... seems to imply a great extension of the northern plain. The geography of the far North is discussed in V. 270-2, but since it is impossible to say how my father came to conceive it I discreetly omitted all indication of the Iron Mountains and Thangorodrim from the map drawn for the published Silmarillion.' Christopher Tolkien

However that hasn't stopped others, using such details as exist, from trying to make maps of the far North -- like KW Fonstad for example, who published a book of maps about Tolkien's World.

If you want to see what Tolkien himself indicated however, I would point you to The History of Middle-Earth volumes, especially The War of the Jewels and The Lost Road And other Writings (the latter being volume five, as Christopher mentions above). Tolkin's own map as reproduced in The War of the Jewels shows more of the North than Christopher Tolkien dared to for the 1977 Silmarillion (given the confusions noted).

Another example of the unfinished state of the work I'm afraid.