Create Terrain withTerrainData

In a project I have to create Terrain by script,I used the TerrainData interface.For some reason the Terrain's width and height can not be equal.The code like this:

 private TerrainData terrain;
 terrain = new TerrainData ();   
 terrain.heightmapResolution = cDepthWidth+1;
 terrain.size = new Vector3 (cDepthWidth,128,cDepthHeightAdjust);
 
 ter = Terrain.CreateTerrainGameObject (terrain);
 terArr = new float[cDepthHeightAdjust,cDepthWidth];
 terrain.SetHeights (0,0,terArr);

But when I had succeed create the Terrain. I found the width and the height of the Terrain was right.But the array of heightmap (terArr) seemed be compressed. The height/width ratio of the heightmap was incorrect.The width of the heightmap has been compressed. I do not know whatreason causes. Is there something wrong in my code?