Welcome, ninjapenguin !

Placement of human features depends on so very many factors. Scale, sure - the larger the scale (smaller area), the more & smaller items will be shown. But also, WHEN is your setting? What's the culture? An archipelago could do with no roads at all; an underground city could technically be nothing BUT roads :-). The purpose of the map would matter too -- a topographic map or the like could make do with just enough cities and borders to make clear who owns the mountain range, what nations the river connects, and so forth. If 'tis a political map, you may need every settlement above village size. If it's the log of an adventurer, it might have just the places he's passed through.

So -- what's the style you're shooting for, and what's the purpose for your map or maps?