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December 2013 Issue
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Inferring what the map doesn’t tell you

Ace navigator Tim Farrant demonstrates how to glean more information from the map than it appears to be showing

In New Zealand, navigating in the hills usually starts with the NZTopo50 series of maps. Developed, updated and published by Land Information New Zealand, these maps show geographic features in detail and are suitable for a wide range of activities.

But maps are and always will be a simplification of reality. If you wanted a map to be 100 per cent accurate, covering all navigation features in detail it would probably need to be on a 1:1 scale, rather impractical in real life. Additionally, as the world is forever changing – farmers move fences and tracks are often realigned – maps need regular updates to stay current and up-to-date. With this in mind, it is worth noting man-made features as ‘common suspects’ for a map being out of date. Vegetation features can also change frequently as windbreaks and forested areas are cut down or planted since the map was last updated.

To avoid confusion, the best features to use are usually contour features such as ridgelines, gullies and hill tops. But be forewarned; while impassable features such as cliffs, terraces and slips are usually marked on the map with ‘toothed’ black lines, these barriers are often left unmapped in remote areas. Near urban centres, you will often find that toothed black lines represent stop banks but on remote parts of Westland they may represent massive cliffs.

In practice a navigator must often infer what the map doesn’t tell them. These inferred features will be specific to the country being traversed and may be cliffs where contour lines are closely spaced, dense vegetation near watercourses or could be a waist high swamp in flat low-lying areas.

Navigation by inferred features is a skill which is more of an art than a science, but also one which can only be learnt by experience.

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