Aye, you should always determine a game scale first in world coordinates. Depending on the game, one unit can be an inch, a meter, a kilometer, etc. A fair number of people like to use 1 unit equal to one meter since that allows for a good mental connection between the two scales. The default camera range is 5,000 units. Most FPS scaled games don't look beyond 500 meters so .1 meter per unit is also a good scale. In the end, it's up to you to choose a scale based on your design.
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TAZ
"Do you think it is wise to provoke him?" "It's what I do." -- Stargate SG-1