recently went back to AC and finally got all those damn flags!! lol it was pretty tedious, but the map i used was very nice. the link on this guide didnt appear to work, so i thought i would share this.
^The link has each district, the flags are numbered + each gives a picture with a caption detailing where to find them. on the bottom of the page there is a checklist, which i always find very useful while gathering collectables. i should note that i capped the flags as i unlocked the areas, i would do ->
viewpoints - citizens - investigation - flags - assassination
(i found it easier to pinpoint the flags location with less clutter on the mini map)
*each map also has small green dots (with picture + caption) detailing the location of each templar. which i didnt notice until halfway thru my playthru
. it would probably be easier to knock those out as you clean up the flags.