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Benthic Habitat Mapping
Scale is a fundamental concept in mapping any habitat. Determining the appropriate data collection, analysis, and visualization techniques relies on knowing what spatial and habitat scales are needed to address project goals. For the purposes of benthic habitat mapping, spatial scale and habitat scale must be considered. Spatial Scale Spatial scale (also called map scale) refers to the relationship between the size of a feature on a map (a shoreline, for example) and the size of that feature in the real world. This relationship is usually expressed as a ratio (map units : real world units), where one unit on the map represents many times that value in the real world. For example, a scale of 1:400,000 means that a feature that is 400,000 units (inches, centimeters, feet, and so forth) across in real life will take up 1 unit (inch, centimeter, foot, and so forth) across on a map. Such a map would be considered "small-scale" because the ratio is very small (1/400,000). Small-scale maps represent a large area; therefore they cannot be very detailed.
In contrast, a map with a scale of 1:500 means that a feature that is 500 units (inches, centimeters, feet, and so forth) across in real life will take up 1 unit across on a map. This would be considered a "large-scale" map because its ratio (1/500) is much larger than the previous example. Large-scale maps represent a small area and are able to show more detail than small-scale maps. The terms "large-scale" and "small-scale" should be used to refer only to the maps themselves, as defined above. Unfortunately, these terms are often erroneously applied to the scale of a habitat. Habitat Scale Habitat scale refers to the geographic extent of a distinct biological community (such as a seagrass bed) or geological feature (such as a sand bar). Habitat scale must be taken into account when choosing which methods of data collection and visualization are most appropriate. A unique vocabulary can be used to indicate habitat scale.
There are no precise rules for matching particular habitats to either habitat or map scale. Often, the same benthic habitat type (for example, eelgrass) can occupy various amounts of space in different locations, defined as meso or macro scale. This variability reinforces the importance of knowing the scale of the habitat one intends to study prior to beginning the survey. The detail of habitat delineation for a particular benthic habitat map depends upon both the spatial scale of the final map and the scale of the marine habitat under investigation. What is "habitat delineation?" Digital resolution of a habitat, as represented in GIS mapping applications, is related to both spatial and habitat scale of the benthic features under study. For example, when mapping lobster habitat it may be important to distinguish small cracks and ledges in the rock bottom. In order to do this using multibeam sonar bathymetric data, fine resolution (1 to 2 square feet) sonar should be used. As resolution becomes coarser, the ability of the sensor to detect micro scale features decreases.
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