Christmas Island Old Drill Lines Clearing

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. There are no attributes assigned to the data. Disclaimer