Please help to remove unwanted and accidently activated graphic enhancement

I must have pressed some keys or a combination of them and now on two tiles, there is a big white dot that I can't remove. But it's not all, around the dot there are those white squares like it was a settler looking for a place to found a city. Does anybody know how I could remove it? It's really a pain to look at it all the time.

It sounds like BUG mod dot mapping feature. This thread should help:

http://forums.civfanatics.com/showthread.php?t=312895

Alt-X will activate the option to dot map which is what you did on accident. Having done that left click lays down a new dot, right clicking a previously created dot will remove it. Then hit Alt-X again to turn the function off.

Personally I find it extremely useful when trying to decide whether I like one spot over another, especially if I know I'll be overlapping big fat crosses. Yes it is not that hard to do it mentally, but being able to have a visual speeds up the decision making process. I'll often leave the crosses there until I do settle. It also serves as a visual warning sign if another civ settles nearby, that that city plot may either be less attractive or eliminated entirely.

Yep! Thanks so much guys for your quick help!

Also, once you have a dot map, you can toggle it visible and invisible, if you want to keep it handy, by using Ctrl-X.