Hey guys, as I said in my introduction post, I'm a newbie in this map drawing world (and in graphic world too, sadly), so I'm sorry if my question could be silly.
I'm trying to draw my first map and I'm following some (a lot of) guides on youtube to understand how and what I can do with Adobe Photoshop CS6. The problem is that my city should have semicircular roads, I tried to draw a circumference and scratch it out on a half, but using shapes (rectangles, triangles or circumferences) oblige me to get a new Level that I can't modify - unless I wish modify that precise shape that I've just drawn.

I've tried to draw a circumference by myself, but the result is absolutely bad (I've no drawing tablet so I work with my mouse and this is even more hard ). How can I