Where are you located?
There are others on the board who have better informed opinions than me.
My guess, and its only a guess, is that you are alright.
In your shoes, I'd collect old gaming maps. Make sure that none of your symbols are trademarks and make a habit of collecting similar images when you find them. Keep information on the authorship of your collection.
I don't think the old school hex map is a commercial bonanza and I don't think TSR could claim a whole heap of uniqueness.
The problem of course is that there are few clear hard and fast rules. Lawyer letters are more scary to the poor and profitless than they are to established companies. I'd love to see a map collection of purely public domain stuff.
Who thinks your program rocks btw....