Or, if you meant the difference in the sizes of pienalueet, these are probably based on multiple factors. Looking at the map these might include population density, house type (switch to ilmakuva and view the difference between Tikanmäki and Tikantori), also industrial/commercial areas often form their own pienalue (Rautpohja, Köyhänpelto). 
Also for whatever reason pienalueet in what was Jyväskylän maalaiskunta until 2009 are bigger, even in Palokka and Vaajakoski. In rural areas the borders look kind of arbitrary, but they kind of have to be.