Well, since this is your first map...
I'll get to point. First, even though everything is nicely done and stuff, decoration wise- you can see the middle is super narrow. And narrow is bad, very bad. Everything siege tank and a good amount of anti air can make a Terran nearly invincible to a point that other races will just resort to cheese techniques. And even that doesn't work everytime.
Also, the natural is way too far. (Natural is usually defined as the first expansion you can take easily with nearly no effort- and be able to defend it just as easily.), making it very disadvantageous for Zergs and Protosses. That makes two advantages for Terran.
Usually, you balance the map in terms considering 3 things. First, you must understand varieties of strategies that each race can take.
The most important race to consider is Terran, because Terran has weapons of mass destruction of super duper doom. Simply put, rigged- in most cases. Why? Because Terran has the most powerful basic unit, the most longest ranged and the most damaging unit, the most cheapest and most powerful anti air unit, etcetc... But the point is, when you give too many advantages to a race- the map becomes rigged. And thats no good. And it seems like your map is really rigged for Terrans.
On another case, with Zerg, you have to consider how fast you can get a natural base- which considerably changes the mutalisk timing variable (if you even know what that means... it means if you can get a natural faster, you can cut down the time you can collect a set amount of mutalisks.) And if you make the natural too close, it makes the Zerg- rigged. Because Mutalisks are cheap, and capable of the most powerful micro.
And last but not least, Protoss. Protoss usually have a thing or so for a lot of powerful units. They're so powerful that when Protosses have access to more than 2 expansions (natural included), they become rigged. Its also because Protoss have access to upgrades faster than other races, and even simple combinations are powerful. (Of course, in higher levels of play, simple combinations never work.) So you got to consider how easy it is to defend a third expansion. (Usually, close proximity of expansion to main means easy.)
None.