z-axis
See Also: x-axis, y-axis
[coordinate systems] In a spherical coordinate system, the vertical line that runs parallel to the earth's rotation, passing through 90 degrees north latitude, and perpendicular to the equatorial plane, ...
Z-Axis: Third or height axis of a three-dimensional Cartesian coordinate system that crosses the XY axis plane at a 90-degree angle. The Z-axis is normally used to represent elevation above sea level.
z-axis
In a spherical coordinate system, the vertical line that runs parallel to the earth's rotation, passing through 90 degrees north latitude, and perpendicular to the equatorial plane, where it crosses the x- and y-axes at the origin (0,0,0).
If we line up the Z-axis parallel to the Earth's axis of rotation (from North pole to South) and if we line up the x/y axes so that positive X-axis intersects the Greenwich meridian (longitude 0°) we've completely defined (with the exception of a few ...
the axis of the cylinder is parallel to the z-axis) will suffice (similarly, if the desired large field of view is only in the vertical direction of the image, a horizontal cylinder will suffice).
The X-axis of the graph corresponds to the Z-axis of the map-relative level of housing Density. In this case, the spikes in the graph indicate measurements that occur more frequently. Note the relatively high occurrence of density values around 2.
The left figure above shows the result of re-projecting onto a plane perpendicular to the z-axis (equivalent to looking at the cone from above the apex), while the figure on the right shows the cone cut along the solid line and flattened out.
The system has its origin at the mass-center of the earth with the x and y axes in the plane of the equator. The x-axis passes through the meridian of Greenwich, and the z-axis coincides with the earth's axis of rotation.
 See also: Axis, Object, Surface, Coordinate, Image
  
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