ON A BATHY-HTPSOftRAPHICAL MAP OF THE BRITISH ISLANDS. 161 



your Committee are of opinion that the existing Ordnance maps should be 

 utilised. A combination of the Ordnance map with the Admiralty charts 

 presents no difficulties, and in doubtful or difficult cases a co-operation of 

 our two Survey Departments would speedily lead to satisfactory results. 

 Your Committee are happy to be able to report that Sir Charles Wilson, 

 the present Director of the Ordnance Survey, is arranging to insert 

 contours showing the configuration of sea bottom upon the contoured 

 edition of the one-inch Ordnance map, and is prepared to extend this 

 system to tbe whole of the Survey as soon as the means necessary for that 

 purpose shall have been granted by Government. This extension will 

 necessitate a certain amount of bathymetrical survey for delineating the 

 beds of lakes and river channels which has not yet formed part of the 

 operations of the Ordnance Survey. 



3. With reference to general maps on small scales, the Secretary of 

 your Committee has prepared contoured maps of the Loch Linnhe region 

 (including Ben Nevis), and of the country on the Lower Medway, these 

 two districts presenting the extreme features which have to be taken into 

 consideration when preparing a bathy-hypsographical map of the whole 

 of the British Islands. These maps have been tinted experimentally. 



4. Your Committee are of opinion that no adequate representation of 

 the vertical configuration of the lowlands, the lower hill ranges, and of 

 the ocean-bed can be obtained on the proposed scale of 1 : 200,000 unless 

 the contours, up to a height and down to a depth of 1,000 or 1,200 feet, 

 are drawn at intervals not exceeding 100 feet. In some localities it may 

 even become necessary to introduce supplementary contours. These 

 contours, whether they refer to the land or to the ocean-bed, would have 

 to be referred to a fixed datum level, such as that of the Ordnance Survey 

 of Great Britain. 



In the more mountainous parts of the country, contours at intervals of 

 500 feet (as on the one-inch Ordnance map) appear to yield fairly satis- 

 factory results. 



5. The larger lakes would have to be contoured as if they had been 

 drained, a faint horizontal shading indicating their character as lakes. 



6. In some foreign maps (including the new one of the United States, 

 on a scale of 1 : 250,000) the contours are printed in brown, and by this 

 means a fair idea of the configuration of the land may be obtained, 

 especially if the intervals between the contours are small. 



7. Your Committee are, however, of opinion that the intelligibility of 

 he proposed map would be very much increased by the employment of 



tints. In selecting these tints it must be borne in mind that the map is 

 to embrace the whole of the British Islands with the surrounding seas, 

 and that a system of colouring suited to the highlands might utterly fail 

 when applied to the more gentle undulations of the greater part of the 

 country. It may at once be admitted that none of the systems of tinting 

 employed or suggested hitherto has proved thoroughly satisfactory. 



8. The 'natural' method of tinting a map of this description, and 

 that which most readily suggests itself, is to apply one colour to the sea 

 and another to the land, and either to increase the depth of the tints 

 with the height (or depth), or to apply the deepest tints to the least 

 elevated parts of the country. A reference to Maps 1 and 2 proves that 

 very fair results are attainable by this method. In the one case the low- 

 lands and valleys are emphasised ; in the other the mountain-tops become 

 the most prominent points on the map. When tinting a map in this way 



1887. M 



