Admiralty Chart 2649: A Chart Adapted for use with Radar

Extract

Practical experience in radar-assisted marine navigation has shown that the closer one is to the general land areas, navigational seamarks, &c, the easier position fixing from radar information becomes, although some particularly congested and confined waters provide exceptions to this rule. There are usually large numbers of more suitable targets available at the closer ranges, and increased ease of identification results from objects being closer to the observer. The latter effect, of course, arises from initially knowing one's position more accurately, and this in turn is based on the shorter ranges at which bearings and/or ranges are being taken.