Any mathematical calculation occurring in world space measures because of Float’s 32-Bit Floating point values and Floating Point Precision relative to those values.
Max 3.4028237 × 10^38
Min 1.175494 × 10^-38
Performing calculations above 2k distance starts returning less floating point precision. this eventually makes it so that X+Y == X because the precision is so low that it results as 0.
To prevent that, you just shift the world origin point and you can have infinite size maps.
You can use World Composition with origin shifting which allows you to combine many maps to reach the ultimate size that you want, I believe the maximum before things become an issue is 6km x 6km