The New Murrey and Blue blog

If you look at a map showing Lancastrian/Yorkist areas at the start of the war, there is a good degree of congruence with Royalist/Parliament division in the Civil War. Not complete, but fairly similar. The main difference is probably the Yorkist domination of the Welsh marches, which tended to be a bit Royalist in the ECW. In simple terms, the North and West were for Lancaster/Royalists and the South and East for Yorkists/Parliament. (With some islands of exception, obviously.)