The world of River King has 6 main map areas. The main area in the middle is the Stream, where all other maps connect back to. You start out in the Stream area and then branch off towards the others.
Each map that you journey though (except for the Underground Lake) will have a Jizo save shrine, shops, and contests for you to participate in. Some of the errands you receive will require you to venture back to previous maps to talk to someone or catch a specific type of fish.
Unfortunatly you do not get an in-game map, so you will have to memorize the layout of each area. Luckly there are maps located inside of the instruction manual.