From Wikipedia

The battle began with the Persians already present at the battlefield.

Darius had recruited the finest cavalry from his satrapies and from an allied Scythian tribe. Darius also deployed scythed chariots for which he had prepared cleared terrain in front of his troops. He also had 50 Indian elephants supported by Indian chariots.

Before the battle, Darius ordered bushes and vegetation removed from the battlefield, to maximize the chariots' effectiveness.
location determined by determined by Sir Aurel Stein in 1938 (see his Limes Report, pp. 127-1.)
proportions determined by description of Darius' 4000 yard main line

Darius placed himself in the center with his best infantry (the Greek mercenaries and his guard infantry the "Apple Bearers"). On both flanks were the cavalry. Bessus commanded the left flank with the Bactrians and Scythians and Mazaeus commanded the right flank with the Syrian and Median cavalry.

Alexander commanded the Macedonian right flank himself, with the Companion cavalry and the Hypaspists, and Parmenion the left flank, with the Thessalian and Greek allied cavalry. Both flanks were protected by lightly armed troops, such as the Agrianians on the right. In the middle stood the Macedonian phalanx infantry in two lines, forming a "double phalanx". The second line was to turn around if out-flanked by the Persians.

The Macedonians advanced, as if entering the trap laid before them. Suddenly the whole army changed direction and started to move to the right, taking them away from the prepared ground. Darius now launched his chariots, some of which were intercepted by the Agrianians.

Darius ordered his left wing cavalry to encircle the Macedonian right and stop their rightward movement. This was countered by Alexander's Greek mercenary cavalry. As more Persian cavalry tried to encircle the Macedonian right flank, Alexander committed his last cavalry reserves to charge the point where the main Persian line joined the flanking cavalry. This caused a gap in the Persian line. Alexander turned his line and charged this gap with a wedge consisting of the Companion cavalry and the Hypaspists. The pursuing Persian cavalry was pinned down by peltists hidden behind Alexander's cavalry. It then advanced directly at Darius himself.

Darius now saw his left flank crumbling and the Macedonians advancing, in order to kill or capture him. He turned around his chariot and fled from the battlefield. The cavalry on the left followed him in his flight.

I just did a modified post of Alexander's Battle of Gaugamela. In it I used an overview map by Lendering, which matches the terrain pretty well with the location of Gaugamela close to other postings and maps. I then took your detailed maps and tried to fit them in to where I thought the battle was fought. I am just a history buff, not an expert. Would like to see what you think.

My post is: http://bbs.keyhole.com/ubb/download.php?Number=783809

I also have one on the Campaigns of Alexander the Great:
http://bbs.keyhole.com/ubb/download.php?Number=203594