QGIS $area field calculator always produces NULL

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Error occurs under Windows in QGIS 2.8.3 and 2.10.1Answers to similar questions eg 57418 have not helped.

The shape file in question was created as follows:
Vector/GPS/GPS tools/Load GPX file (Routes)
Layer / save as ESRI shape file [....\epsg4326\routes.shp

The failing sequence is:
Start a new map/add vector layer [routes.shp]
Open attribute table
Add new column AREA [decimal real width=17 precision=8]
Manually edit both AREA values to verify format.
Select all entries [2 entries]Field calculator / existing /AREA / geometry / $areaAlways get NULL

I have tried countless combinations of width and precision for AREA. I have installed/reinstalled different releases to no avail.

What's up Doc?

PS: Beginning to smell a rat in the direction of either the GPS tool or the shape file. Starting with the shape file, how may I independently verify it!



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