而昨天我向你们讲过，这种种情况下，如果用笛卡尔坐标系描述是有意义的，等于1,0，和，- 1，时，m, equals, one, zero, and, minus, one，说明这三个原理其实性质是相同的。

And I showed you last day that this is one case where trying to go in a Cartesian space makes sense, m indicates the three principle coordinate directions.

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例如，当我们徒步走在空旷的乡村上的时候，我们发现使用地理方位非常有用。 但是当我们描述小规模的空间时，我们完全以自己为中心的坐标系进行交流。

We find it useful to use geographic directions when hiking in the open countryside, for example, but the egocentric coordinates completely dominate our speech when we describe small-scale spaces.

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下面的图表描述了几种常见的方法在坐标系中的位置。

The following chart illustrates where several popular methods appear along these dimensions.

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