UV Map - Changes direction midway I hope that will be my last question about UVs in blender. 

I now have an object unwrapped. The Quads are sometimes not exactly squares. On one site they get smaller so its a trapeze. Therefore when the UV is a normal square the uv tiles should get smaller to the smaller site of the square but in my case they are randomly changing direction like it can be seen in the image. 





Here is my blender file so that you can look up my UV:

BlenderFile
This is a problem related to uv coordinate interpolation. It is inevitable when working with very low mesh density. To avoid
this kind of problem increase mesh resolution by adding few extra loops. 

As you can see the distortion runs along triangles - this is the way uv is interpolated in quad polygons.