均角投影圖

Isometric projection is a form of graphical projection — more specifically, an axonometric projection. It is a method of visually representing three-dimensional objects in two dimensions, in which the three coordinate axes appear equally foreshortened and the angles between any two of them are 120°. Isometric projection is one of the projections used in drafting engineering drawings.
The term isometric comes from the Greek for "equal measure", reflecting that the scale along each axis of the projection is the same (this is not true of some other forms of graphical projection).
One of the advantages of isometric perspective in engineering drawings is that 60° angles are easy to construct using only a compass and straightedge.
[edit] Visualization


圖片參考：http://upload.wikimedia.org/wikipedia/commons/thumb/f/f7/Perspective_isometrique_cube_gris.svg/142px-Perspective_isometrique_cube_gris.svg.png



圖片參考：http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png
An isometric drawing of a cube. Note that the perimeter of the 2D drawing is a perfect regular hexagon: all the black lines are of equal length and all the cube's faces are the same area.
Isometric projection dictates the direction of viewing in that the angles between the projection of the x, y, and z axes are all the same, or 120°. For objects with surfaces that are substantially perpendicular to and/or parallel with one another, it corresponds to rotation of the object or camera by +/- 45° about the vertical axis, followed by a rotation of approximately +/- 35.264° [= arcsin(tan(30°))] about the horizontal axis, starting from an orthographic projection relative to an object's face (a perpendicular view to a face of an object).
Isometric projection can be visualized by considering the view of a cubical room from an upper corner, looking towards the opposite lower corner. The x-axis is diagonally down and right, the y-axis is diagonally down and left, and the z-axis is straight up. Depth is also shown by height on the image. Lines drawn along the axes are at 120° to one another.


[edit] "Isometric" projection in video games and pixel art


圖片參考：http://upload.wikimedia.org/wikipedia/commons/7/71/Pixelart-tv-iso-2.png



圖片參考：http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png
A television set drawn in near- isometric pixel art. Note the 2:1 pixel pattern ratio in this zoomed-in image.
In the fields of computer and video games and pixel art, axonometric projection has been popular because of the ease with which 2D sprites and tile-based graphics can be made to represent a 3D gaming environment. Because objects don't change size as they move about the game field, there is no need for the computer to scale sprites or do the calculations necessary to simulate visual perspective. This allowed older 8-bit and 16-bit game systems (and, more recently, handheld systems) to portray large 3D areas easily. While the depth confusion problems illustrated above can sometimes be a problem, good game design can alleviate this. With the advent of more powerful graphics systems, axonometric projection is becoming less common.

[take a look from http://en.wikipedia.org/wiki/Isometric_drawing ]