What do Latitude Longitude Changes Mean in Real Life?

When dealing with decimal Lat/Long, a change in the 5th decimal place results in the following changes:

a 0.00001 change in Latitude results on a change of ~ 1.11m

a 0.00001 change in Longitude results on a change of ~ 0.926m  (at my location)

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I used the formula from this webpage:  http://social.msdn.microsoft.com/Forums/is/csharpgeneral/thread/36559707...

There are several ways to do this depending upon how accurate you need your measurement to be.  For long
distances you will need to use the arch length between the two lat/long points for your calculation.

For shorter distances, not too close to the poles, one fast technique is to use one of the lat/lon points you
get back as the origin to an orthogonal plane.  We can call this point P.

For any given P, we can calculate a scaler conversion for changes in lat/lon. We are lucky because one of the values never changes.

MeterPerDegLat = 40008000 / 360.0;

MeterPerDegLon = 40075150 / 360.0 * cos(P.Lat * PI / 180);

We can calculate the distance between Q and P very quickly:

 X = (Q.Lon - P.Lon) * MeterPerDegLon;

Y = (Q.Lat - P.Lat) * MeterPerDegLat;

Dist2 = X * X + Y * Y;

To save computational time, you don't need to calculate the square root if you are doing a comparison.  It is better to square your threshold value.

 Which results in something like this using HDOP:

MaxDistInMeters = 5 * HDOP;

MaxDistInMeters2 = MaxDistInMeters * MaxDistInMeters;