Abstract This paper was originally presented to the 48th ANZAAS Conference held in Melbourne between 29th September and 2nd October, 1977. It describes the programs undertaken by the Division of National Mapping to delineate mean low water and mean high water coastlines. Remote sensing techniques using black and white infra-red aerial photography have been adapted to provide a means to accurately locate and identify the waterline at the instant of MLW and MHW. Ground truth testing complemented the photography to aid interpretation while the determination of the instant MLW and MHW was approximate within specified intervals which were dependent upon the physical characteristics of the tide and coastline. Mean High Water line is the line drawn on Topographic maps to show the interface of the land and the sea whilst the Mean Low Water line is the same interface shown on Bathymetric maps. It is also used for territorial boundary purposes. The Division of National Mapping in the Commonwealth Department of National Resources is the Australian Government's civilian mapping agency. It is responsible, in co-operation with the other members of the National Mapping Council, for the production of topographic maps over the whole of Australia. The Division's mapping program has seen the production of several map series, the International Map of the World (IMW) Series at 1:1 million scale and two topographic series at 1:250,000 and 1:100,000 scales. The 1:100,000 series is only part complete whereas the IMW and 1:250,000 series are already complete with second editions already published. Map quality depends upon specifications and standards of accuracy and the standards applying in Australia today require depicted detail to be correct to within half a millimetre on the map. This means that detail must be fixed to within 125 m on the ground for the 1:250,000 scale topographic map but the same detail must be fixed to within 50 m of its true position on the ground for the larger scale 1:100,000 map. This is the essential requirement that dictates the ground survey techniques that must be used for compilation control. This paper discusses how we at National Mapping have dealt with the problem of identifying and plotting the coastline on our topographic maps. The ubiquitous blue line which depicts the land/sea interface has a much lesser significance at 1:250,000 scale than it has at 1:100,000 scale, so that where there was no problem with the former series we found we were faced with a real one for the later 1:100,000 series. The real problem resulted from the accuracy requirement which meant that a discerning survey technique would be required and, of course, an appropriate definition for the coastline would also be needed.