First of: Almost the entire (Real) world uses the Metric system so please, even thought the most persons are US american here, use an measurement people outside the US (like me) can understand.
Second an Bigger world would employ more "discspace". That is proportional to the size of the map + the ammount of creatures and People. DF would only need an way to get the "free" space on your disc.
Since Miles were used in this thread
i am rolling with it.(BTW: 100 miles = 161 Kilometer)
(edit: I hope my calculations are correct if not tell me.)
The amount of discspace one big Map allocates was around 4MB without fortresses. 512^2 would be 16MB, 1024^2 = 64MB, 2048^2 (or 640000 Mē = 800*800 Miles) Maps = 256MB etc. The world has an surface of 320 MIO Mē in df it would be only
87040 12800 MB (= 320MIO Mē/(100M*100M) * 4 MB) or
85 125 Gig.
If you use some tricks you can cut even the amount of calculations and "lag" while playing. For example you only have to track the populations of an certain part of the world while you are playing - the part you are in. You too only have to have this areas loaded into the Memory. Lets say, as long your actions have only affect on an certain area you dont need to track persons from other continents
.
Large "crouds" and Areas can be abstracted as long they are offscreen for most calculations without loosing the individual data. The same goes for products etc.
And were are tricks i dont even know to cut the mass of calculations.
The loadtimes on the embarkscreen would increase and the lenght of the worldcreation. To create an "realworld" sized World (510 Kmē/320Mē without history) it would be around
302 111 days if your normal (256*256) map gets calculated in 5 Minutes.
Well google offers using not used clockcicles for Cloudcomputing so with an bit memory hacking and if anyone gets out how the mapfile is "constructed" you could create an DF world as large as the real and play it. Or maybe someone has acces to an Cluster in an University / Computing center?
Interresting if i use the 100 Miles for an Map an "Tile" has as Side-lenght of 628,9 Meter (= 161 KM / 256). If this tiles consists now each from 48*48 tiles itself iirc. So this "Fort-"Tiles have must have an sidelenght of 13.1 Meter(=(161KM/256)/48).
No wonder that an Dragon and Collosi fit in one Tile but wagons wich are 40*40 Meter?