Quadrant tab

The Quadrant tab corrects incorrectly positive latitude and longitude values during import.  This is mostly used to change incorrectly positive longitude values for North America.  

Background

The spherical surface of the Earth is divided by east-west running lines of latitude and north-south running lines of longitude.  The equator that defines 0∨dm; latitude is defined as the plane perpendicular to the Earth’s axis that also contains the Earth’s center of mass.  The Prime Meridian that defines 0∨dm; longitude is a arbitrary line that runs through the Royal Observatory in Greenwich, London.

By convention, the equator is 0∨dm; latitude, with +90∨dm; at the North Pole and -90∨dm; at the South Pole.  The Prime Meridian is 0∨dm; longitude with positive longitude to the east and negative longitude to the west.  The equator and the Prime Meridian therefore divide the Earth up into four quadrants.  The signs of latitude and longitude distinguish between the four qquadrants.  Western Europe, Russia, China, and the Middle East have positive latitude and longitude.  North America, on the other hand has positive latitudes and negative longitudes.  As an example, (+29.97, -95.35) is Houston, TX, while (+29.97, +95.35) is Byai Zhen near the Tibet-India border.

Quadrants and LatLon Signs

Despite the convention, LatLon points (particularly in North America) are prone to being reported as having positive longitudes when they should be negative.  This error can cause overlay data to grossly misalign, and to effectively “flip” the east and west sides of the map. A mix of correctly and incorrectly formatted LatLons will strand some data literally in the next hemisphere.

Using the Quadrant tab

The Quadrant tab automatically converts incorrect positive LatLon values to the correct negative values for the selected quadrantduring import.  This is primarily used for projects in North America, where longitude values are commonly incorrectly reported as positive.  Selecting the NW quadrant, for example, will convert all incoming positive longitude values to the correct negative longitudes, where the incorrect (+29.97, +95.35) would convert to a correct (+29.97, -95.35).

Most latitude and longitudes for the rest of the world are reported correctly.  As such, users working on international projects should select the NE quadrant.  This quadrant, being north of the equator and east of the Prime Meridian, has both positive latitudes and longitudes.  When this quadrant is selected, no correction is made.