Maurizio,

GPS, of course, is now used to site boundary markers during the
demarcation and maintenance phases.  It would be very useful during the
delimitation too insure that surveyors and boundary commissioners go
into the field to take readings of anticipated turning points.  This is
particularly important where cadastral boundaries are supposed to mesh
with international boundaries (One should also cite in the
treaty/decision, whether the cadastral line or the delimited line takes
precedence in the event of a dispute during the demarcation).

If the delimitation agreement/decision associates coordinates with
features, the document should clearly state that the feature location
should take precedent over the derived coordinates in the event of a
conflict.  Some "fudging" room of so many meters in either direction
must be built into the delimitation agreement/decision for the
demarcation surveyors and monument builders to make adjustments at the
proposed monument site.

Unless the proposed land boundary is supposed to run in straight line
segments over vast tracts of open, sparsely-inhabited land real estate,
I would argue against listing just coordinates --even with GPS derived
one-- in the delimitation and select obvious elevation features, ridges,
and drainage for turning points and lines.  This principle appears to
have served the British very well in establishing colonial boundaries.
They (and their post-colonial independent states) got into trouble with
long straight line segments and coordinate-driven turning points.

Unnamed hypsographic features can be identified with coordinates, but
their location caveated with 'located approximately at' (and why not
hyperlink a photo, just to be on the safe side?), as even the
large-scale maps and orthophotos have unstated but built-in horizontal
inaccuracies up to 50 meters or more.  Furthermore, hasty spot GPS
readings during the delimitation survey may turn out to be inaccurate.

Streams are less desirable as boundaries, as Stephen Jones indicates,
but if used, the location of the boundary therein should be specified.
The use of 'thalwegs' in wide-streamed wadis and other intermittent
riverbeds in areas subject to prolonged drought and flash flooding
should be avoided, and one should resort to coordinates instead of
finding a wind-blown channel.

One should likewise avoid appointing man-made features (city limits,
rail lines, wells, barns and the like) and flora (old oak trees, olive
trees, etc) as turning points; and especially in cases where cadastral
surveys already exist, I would again advocate coordinates taking
prededence in the delimitation.

Where long-straight lines are involved, I would spell out --even in a
land boundary delimitation agreement/decision-- whether a loxodrome or
geodesic line is intended.

Finally a comment on marker versus coordinate: in my discussions with
the Canadian and U.S. boundary commission members, one of the humorous
down sides of  the ready availability and low cost of hand-held GPS
receivers is that (usually) men receive them as gifts from spouses --
desperate to find a new toy less dangerous than a chainsaw-- who after
siting their bathrooms and property lines go up to the border to take a
reading of their local markers.  The result is a deluge of mail to the
Commission from guys indignant that their local boundary markers do not
reside precisely on the 49° parallel according to their GPS readings.
Our treaties stipulate that it is the location of the marker during
emplacement that dictates the location of the boundary.  Granted that
the early astronomical surveys were off a bit, but a $49.95 GPS receiver
is also inaccurate, even after averaging multiple readings.  I hope the
newly independent states delimiting and demarcating their new boundaries
have such clauses in their treaties.

A good question you posed, Maurizio.

Regards
Ray

Ray Milefsky, Specialist
International Boundaries and Sovereignty Issues
Office of the Geographer and Global Issues
U.S. Department of State

Maurizio Morabito wrote:

> Pardon me, this surely is an amateurish question, but
> is there any project to use GPS to define boundaries?
>
> I am sure there would be plenty of space in the future
> for arguments about centimeters of difference
>
> regards
> maurizio
>
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