180° of longitude are marked off east of the Prime Meridian, and another 180° west of it.
You're free to draw in as many reference lines on your map as you'd like. There's no
set number of lines, that you have to pick one from when you measure the longitude
of a place.
W
Longitude or meridians are the distances in degrees measuring east or west of the prime meridian.
Longitude,the angular distance east or west of the prime meridian.
It is neither. The prime meridian is 0 degrees longitude. All other meridians are measured from this. East or west to 180 degrees.
The Prime Meridian is numbered zero degrees. Meridians, or lines of longitude, are numbered with increasing numbers of degrees both east and west of the Prime Meridian. On the opposite side of the world from the Prime Meridian is 90 degrees, which is also the International Date Line.
Longitudes west of the prime meridian are given either as "40 degrees W" or "-40 degrees", with degrees represented by the "o" degree symbol.
Longitude lines. They are also called meridians.
The only lines that can run parallel to the Prime Meridian on any map are other meridians of longitude, and the only map on which they can be printed parallel to it is a Mercator Projection. They are not really parallel to the Prime Meridian.
They are measured east and west of the Prime Meridian. They run north-south across the globe from the North Pole to the South Pole.
Meridians of Longitude All of the other meridians; the lines of longitude.
That's going to depend on how you're holding your map or globe. -- If the north pole is at the top, then meridians to the left of the Prime Meridian mark west longitudes. -- If the south pole is at the top, then meridians to the left of the Prime one mark east longitudes. -- If the north and south poles are toward the sides of the map, then the Prime Meridian is a horizontal line between them, and there is nothing on Earth to the left or right of it.
The meridians of constant longitude mark angles east or west of the Prime Meridian. Distances can't be estimated with only that information.