Determining the distance of a city from the equator requires some basic math and a small amount of research. The earth is not a perfect sphere but is actually flatter at the poles than at the equator, so the circumference around the poles is slightly shorter than the earth's circumference at the equator. Luckily, the difference is small and so calculations of distance that assume a spherical earth are accurate to within about one per cent.

Use metric measurements to do your calculations and if you wish you may convert to miles or feet later. The circumference of the earth through the north and south poles is 40,009 kilometres (km). The earth, like any circular object, can be divided into 360 degrees. There are 90 degrees of latitude between either pole and any point on the equator, so because 90 is 1/4 of 360 (360 / 90 = 4), we know that the distance from the equator to either pole is 1/4 of 40,009, or 10,002.25km. Another way to think about this is that each degree of latitude is roughly 111km in distance (40,009km / 360-degrees = 111.136km).

Determine the latitude of the city whose distance from the equator you wish to know. Latitude is measured in terms of degrees north or south of the equator. Many websites and search engines can help you determine latitude, including online mapping software or government resources such as the National Oceanic and Atmospheric Administration (NOAA) website. Typing your city and state into the NOAA's search bar will return the latitude and longitude of that city within the first few results. Without access to the Internet, you can find the coordinates by inquiring at your local library or airport.

Divide the degrees of latitude of your city by 90 and multiply the quotient by 10,002.25. The resulting number is the approximate distance in kilometres of your city directly north or south from the equator. For example, if we want to determine how far north of the equator is Columbus, Ohio, we would use the latitude of 39.98 degrees North, according to the U.S. National Weather Service, and calculate the distance using this formula: (39.98 / 90) X 10,002.25 = 4,443.22km. Because we determined earlier that each degree of latitude or longitude is equivalent to a little over 111km, you may also multiply the degrees of latitude by 111 to get a rougher estimate of the distance. Try it on your own to see the difference in your answers.

Convert to miles, if you wish, by dividing the distance in kilometres by 1.6093, which is the number of kilometres in one mile. To convert kilometres to feet, complete the kilometres-to-miles calculation and then multiply by 5280, which is the number of feet in one mile.

#### Tip

The measurement system described is accurate to within 1 per cent assuming the earth's vertical circumference at 40,009km.

#### Tips and warnings

- The measurement system described is accurate to within 1 per cent assuming the earth's vertical circumference at 40,009km.