People fail to realize that elements in an isometric scene can be rotated and viewed from different sides. I see the center land mass as being an octagon. Funny thing is all you would need to do is add some more bridges and people would call it isometric. It seems that the ratio of skewing is correct for all your squares. People fail to understand that shapes may be viewed in an isometric grid but do not have to be aligned with the x and y grid. Things may be rotated even in isometric perspective. If your player moved twice as fast along the width of the screen as he moves along the height of the screen it would be isometric. There is no way to prove this is or isn't iso without an initial image. We need to see what distortion has taken place and use this as a ruler. The orthographic pixel art isometric grid consists of grid squares twice as wide as they are tall. People have a hard time thinking about isometric views but If they were told to draw an organic shape in "isometric" view they would be lost and could never prove that it is in the proper view without some trigonometric proofs. People expect to see corners in isometric and if the sides of shapes aren't aligned with an axis they just don't understand it as being isometric. If you rotated a cube along the z axis they would claim it isn't isometric but it still would be. The view is the camera's height from the point (0,0,0) paired with the downward pointing angle. My advice for anyone that doesn't understand isometric is to go into a 3d program and rotate a simple cube in isometric projection. The shapes' rotations do NOT directly effect the view, the view effects the shapes. You can rotate a shape in ANY direction while not changing the view. Technically an isometric cube can be rotated and not have any angled lines as you have done for your tiles.

 

I'll provide some proof later.

@ Spartan

Isometric projection has nothing to do with shading. There are many shading models you can use. Atmospheric shading coupled with distance and direction shading are what you are probably thinking of. You can still apply atmospheric effects like fog and directional lighting to iso. Look at any good CAD/CAM renderer and you will see. An ambient shading model would provide what you are refering to. Why would you draw hidden shapes at all though? 

 

@ Others

 

Planometric simply means that one face in a series of cuboids is algined with the XY plain. There are 3 coordinate planes in isometric. XY, XZ and YZ. Planometric views are limited to shapes that are cuboids. Planometric has one mathmatical plane and 2 imaginary depective ones. All shapes can be defined in isometric planometric has nothing to do with rotation. As Jalonso has said there is no perspective distortion but there is a set perspective. It can only be understood by human draftsmen not computers. You cannot draw some shapes in planometric it is not a purely mathematical coordinate system. You can however draw all shapes in isometric. Isometric refers to the rotation and position of the camera NOT the shape. Depending on the position of the cube you might see as few as two or even one of its faces. The camera would still look down at the proper angle and would not move.

Planometric is just a faulty system used to describe simple shapes for draftsmen.