Surveying & Built Environment Vol. 22 Issue 1 (December 2012)

INTRoduCTIoN
The Demarcation District (DD) Survey
was a comprehensive boundary survey
which covered the New Territories
between 1899 and 1905. A DD Sheet,
under the deeds registration system, is a
registered plan with a boundary clause
stating that the lot boundaries were
“particularly delineated”.
There is no spatial coordinate
framework on a DD Sheet. The geodetic
control information of the DD Survey
has been unavailable in recent decades.
Thus, the exact positioning accuracy of
DD Sheets cannot be checked directly.
In a plane-table survey done in the
period of 1900’s, the survey plan could
possibly claim a good accuracy up to 1
mm. It means that the surveyed features
are drawn accurately on the plan which
is within 1 mm on the plan to the ‘true’
position. Accumulated professional
experience and research results on using
DD sheets indicate that field bunds in
a good accuracy DD sheet should have
achieved the 1 mm accuracy within
a standard deviation (Zhang & Tang,
2012).
Much that has been published on
the DD Sheet, (Leung et al, 2008)
confirms its nature as the product of a
land occupation survey. This theme is
followed in this paper. The reliability of
the inherent graphical accuracy of DD
Sheet is analysed. And, it is suggested
that the agricultural occupation pattern
should be used to reasonably represent
the DD images.
Surveying and Built Environment Vol 22, 74-87 Nov 2012 ISSN 1816-9554
dIRECT
GEo-REfERENCING
dd SHEET WITH
fIEld SuRVEYING
CooRdINATES
Direct geo-referencing means that
the coordinates’ control information
is applied directly onto the selected
features of the un-coordinated plan
image. The basic principle is to find
out the coordinates of some significant
landmarks on the DD Sheet providing
that a feature that existed in 1905 can
still be seen as the same intact land
boundary feature today. The georeferencing
function of a Geographic
Information System (ArcGIS 9.2 is
used in this project) applies the current
coordinates of the selected features
to the corresponding features on
DD Sheet. In theory, given the scale
and the north direction, one control
point (define x and y coordinate) is
sufficient to determine 4 parameters
in a horizontal datum. However,
after the DD Sheet scanning, the
scale and direction information need
to be defined again. So, at least two
control points are needed to perform
DD Sheet geo-referencing. Different
numbers of control points and different
transformation algorithms will give
different results. This paper gives
examples using a subject area in the
Kam Tin Demarcation District Sheet
(DD 109) as shown in figure 1.
SBE
75