The range of values and representation of latitude and longitude have several conventions.
There are two common conventions for the sign of the numbers. On maps and in many documents latitudes north of the equator are listed with a N or S after the number. These designate the northern and southern hemisphere. Sometimes the author of a document or map just assumes the user knows which hemisphere is being used.
For computers the numbers are written as signed numbers. The official convention is for North Latitude to be positive and South Latitude to be negative. Thus the south pole is either 90 S degrees or - 90 degrees.
The letters designating longitudes are W for west and E for east. The zero line is the prime meridian which runs through Greenwich England. Again the letter is sometimes left off. This is common in the United States where West Longitude is assumed.
Signed Longitude is more confusing because you can add or subtract 360 degrees to any longitude and get an equivalent angle. The official scientific convention is that East Longitude is positive and West Longitude is negative. Thus the Empire State Building is at 74 W or -74 degrees using this convention. But it is also 286 E. This is because 284 = 360 - 74. The relationship between East and West Longitudes is
Longitude-East = 360 degrees - Longitude-West
But, the US Geological Survey (USGS) and he US National Geodetic Survey (NGS) use a sign convention with West Longitude positive. In general, documents and computer programs in the US meant for the public use this convention. Programs and documents for scientific purposes usually use East Longitude as positive. (This gives a right hand coordinate system). But to be sure, you just have to read the documentation.
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