In early 2011 PRL provided Geoscience Australia with the Old Drill Hole Clearing dataset.
This dataset shows the location of old drill lines cleared through the rainforest on Christmas
Island. Drill lines were cleared to test the land for phosphate deposits and were cleared from
the 1950’s through to the 1970’s, before Phosphate Resources Limited (PRL) began mining
on the island.
The Old Drill Hole Clearing dataset has been developed from the Peg and Line grid. PRL used Surpac to create a road outline 7 m wide (this is the
estimate of two dozer D6 blades widths) along each of the previous drill lines. They were
then stitched together and made into a polygon.
There seems to be a good correlation between the extent of the drill lines and evidence of
clearing from the 1987 orthophotography.
The accuracy of the Peg and Line used as a base when the shapefile was produced is of
relevance. The error in the data appears to be in the vicinity of 100 metres. As clearing
boundaries and coast (though highly simplified) of the same map plot in far better position
(after transformation) in relation to the orthophotographs and other GIS themes, the majority
of inaccuracy in this theme is probably inherited from the original map (abbsite.dwg). That
is, it appears that the clearings and coast of abbsite.dwg are reasonably accurate though very
imprecise (intended to be viewed at much greater scale), while the line and peg grid appears
less accurate. Thus the grid on the GIS is mainly illustrative at this time.