A good way to find out 'position scarcity' quickly is to get a positional ranking list w/ stats. The 'fault lines' between different degrees of quality should be readily apparent. Generally, except for the first few rounds, you are best off to wait until the lower levels of a given tier of players to grab a guy. I also characterize the 'best' guys as 'stars' and include them in the first tier, rather than allocating a separate tier for the top performers. To me, this seems to provide a more accurate 'measurement' of positional depth than having a short list of guys at the top and some (in the case of, for example, OF where you have a LOT of very good guys in the second tier...)
For example, if you have 'punted' the 1st Rd 2B, you do not necessarily NEED to grab a second tier guy right out of the door either. That way, when you are 'punting' 2B, you can ride it and stock up on quality players elsewhere before going back for a lower tier guy who will, in most cases, put up numbers comparable to the guys at the start of a given tier. If you do this, you will notice some categories of guys who may be of use who are way off of any of the top 100 or top 200 charts but would still be able to put up say 10-18 HR, hit .275 w/ some RBI and maybe some steals too. Doing a bit of research and IDing a 2B candidate in a lower tier, who can nonetheless maybe pull off 10 HR and 25 or 30 SB w/o killing BA can be more of a critical call than whether to pick Pujols or Arod w/ your first pick.