there's a noun conjugation called Ukubwa and Udogo, which is basically derivatives of nouns that are the "bigger and smaller versions" of the regular noun e.g. a town is mji (regular), a city is jiji (ukubwa), and a village is kijiji (udogo). A house is nyumba, a room is chumba, and a mansion is jumba

So Ukubwa nouns are in the Ji/Ma class while Udogo nouns are in the Ki/Vi class. This conjugation only applies to some nouns, here is an article with some more examples: http://swa.gafkosoft.com/ukubwa_na_udogo

Hope this helps! (And uwanja is a field or plot, kiwanja is on a smaller scale, like a playground)