以下，是GRE官方指南(OG)中有关什么是按照比例，什么不是按照比例绘制的说明(或者说是important assumptions)

　　1. Geometric figures, such as lines, circles, triangles, and quadrilaterals, are not necessarily drawn to scale. That is, you should not assume that quantities such as lengths and angle measures are as they appear in a figure. You should assume, however, that lines shown as straight are actually straight, points on a line are in the order shown, and more generally, all geometric objects are in the relative positions shown. For questions with geometric figures, you should base your answers on geometric reasoning, not on estimating or comparing quantities by sight or by measurement.

　　2. Coordinate systems, such as xy-planes and number lines, are drawn to scale; therefore, you can read, estimate, or compare quantities in such figures by sight or by measurement.

　　3. Graphical data presentations, such as bar graphs, circle graphs, and line graphs, are drawn to scale; therefore, you can read, estimate, or compare data values by sight or by measurement.

　　简而言之就是：几何图形未必按照比例绘制，但是坐标系和图表题是按比例绘制的。(我知道你可能直接跳读到这句话了……)

　　我的解读是，官方给的几何图一般画的还是比较准确的，但是如果你要是根据自己的估值去进行比较、计算等，然后犯了错误，那可就不怪我ETS了，因为我说了绘制的不一定准哦。我们的图表题和坐标系(实数轴和平面直角坐标系)画的可是准的，你可以估值的，然后用在接下来的运算中是没有问题的(注：如果涉及到大小比较的话，也要警惕一下，我们稍后说)。

　　所以面对几何题目，如果涉及到比较边长，比较角度大小等，一定要警惕。