<story><title>111,111.1 meters is reliably 1 degree of latitude</title><url>https://gis.stackexchange.com/a/2964/5599</url></story><parent_chain></parent_chain><comment><author>delta_p_delta_x</author><text>The metre was re-defined[0] in 1791 as one ten-millionth of the quarter-meridian, or ninety degrees of arc, through Paris.&lt;p&gt;It then follows straightforwardly that 1° ≡ 1&amp;#x2F;90 × 10^7 m = 111 111.111... m.&lt;p&gt;It also follows straightforwardly that the circumference of Earth is approximately forty million metres, or 40 000 km.&lt;p&gt;[0]: Edit: the initial definition of the metre was the length of a seconds pendulum, i.e. the length of a pendulum with a period of two seconds.&lt;p&gt;Given the formula &lt;i&gt;T&lt;/i&gt; ≈ 2&lt;i&gt;π&lt;/i&gt;√(&lt;i&gt;L&lt;/i&gt;&amp;#x2F;&lt;i&gt;g&lt;/i&gt;), letting &lt;i&gt;T&lt;/i&gt; = 2 and &lt;i&gt;L&lt;/i&gt; = 1, we have 1 = &lt;i&gt;π&lt;/i&gt;√(1&amp;#x2F;&lt;i&gt;g&lt;/i&gt;), and 1 = &lt;i&gt;π&lt;/i&gt;²&amp;#x2F;&lt;i&gt;g&lt;/i&gt;.&lt;p&gt;This is also why &lt;i&gt;g&lt;/i&gt; is so close to the value of π²—because the former is expressed in units that are &lt;i&gt;defined&lt;/i&gt; that way. It&amp;#x27;s also not a coincidence that 1 cm³ of water is 1 g—for a long time, that was the &lt;i&gt;definition&lt;/i&gt; of the gram.</text></comment>
<story><title>111,111.1 meters is reliably 1 degree of latitude</title><url>https://gis.stackexchange.com/a/2964/5599</url></story><parent_chain></parent_chain><comment><author>gp</author><text>1 nautical mile (~6076 ft) is exactly one minute of arc at the Earth&amp;#x27;s equator.&lt;p&gt;As a sailor, I wish that all miles were nautical miles because they have a real meaning. What good is 5280 feet?</text></comment>