Where? In the US? England? Canada? or ... ??
They are usually created/changed by population, not geographic size.
why do legislative districts vary so muc in size?
3 answers
In the U.S., legislative districts at all levels of government are drawn according to population. Therefore, urban areas with dense population will have smaller districts in geographic size compared to sparsely populated areas. Each district is to have roughly equal population.
noob.