Use numerals and lowercase to identify the imaginary locater lines that ring the globe from north to south through the poles.
They are measured in units of 0 to 180 degrees east and west of the “prime meridian,” which runs through Greenwich, England.
Here are some examples,
- 33rd meridian (if location east west of Greenwich is obvious)
- 1st meridian west
- 100th meridian
See also AP Style Latitude and Longitude