で denotes "action
entirely within the boundaries of an area". For example, "Nihongo で hanasu" (speak in Japanese) and "kawa で oyogu" (swim in a river, or perhaps swim around in a river).
We should also bring up the example of に which means to "travel from within the boundaries of one area into the boundaries of another area". For example, "kawa に oyogu" (swim into a river) and "Kyouto に hikkoshi suru" (move to
Kyoto, in the sense of changing place of residence). Another example is "omawarisan に naru" (become a policeman, in the sense of changing from non-policeman-ness to policeman-ness). (Please forgive my use of the gender-bias word police
man.)
Then there is the usage of へ which means "to move towards an area without actually entering that area". For example, "kawa へ oyogu" (swim towards a river, without actually entering the river). (Please note that in this example, へ is pronounced as "e" not "he").
"It all started when I had fun making pictographs for the kana..... "
--> Don't forget to use the constellation Orion as a way of writing the katakana オ. I think オ is a great representation of Orion with its belt of stars, which looks just like the diagonal stroke in オ. Then there is the use of the English word akimbo to represent ア, which looks just like an akimbo.
"...like cave man."
--> I know lazy people who leave out post-positionals like に and で because these words are "just too much trouble". If we say, "Watashi ikimasu" it sounds like, "Me go! Me take airplane across burning desert!"