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Reasons Why it's Important to Take Good Locality Data

MVZ Handbook > Recording Localities in the Field
Data Quality

“Data are of high quality if they are fit for their intended use” (Juran 1964). As a collector, you may have an intended use for the data you collect. In the museum, the data you collect have the potential to be used in unforeseen ways; therefore, the value of your data is directly related to the fitness of those data for variety of uses. Higher quality locality data can be achieved by following the guidelines given in the “MVZ Guide for Recording Localities in Field Notes”, the justifications for which are elaborated below.

Locality

One purpose behind a specific locality description is to allow the validation of coordinates, in which errors are otherwise difficult to detect. The extent to which validation can occur depends on how well the locality description and its spatial counterpart describe the same place. The highest quality locality description is one with as few sources of uncertainty as possible. By describing a place in terms of a distance along a path, or by two orthogonal distances from a place, one removes uncertainty due to imprecise headings. By choosing a reference point of small extent, one reduces the uncertainty due to the size of the reference point. By choosing a nearby reference point, one reduces the potential for error in the offset distances. To make it easy to validate a locality, try to use reference points that are easy to find on maps or in gazetteers. At all costs, avoid using vague terms such as “near” and “center of”. In any locality that contains a named place that can be confused with another named place of a different type, specify the feature type in parentheses following the feature name.

Locality example using distance and heading along a path

E shore Bolinas Lagoon, 3.1 mi NW (via Hwy. 1) intersection of Hwy. 1 and Calle del Arroyo in Stinson Beach (town), Marin Co., Calif.

Locality example using two cardinal offset distances from a reference point

ice field below Cerro El Plomo, 0.5 km S and 0.2 km W of summit, Region Metropolitana, Chile

Elevation

Under normal conditions, GPS devices are much less accurate for elevation than for horizontal distances, and they do not report the altitudinal accuracy. If elevation is a defining part of the locality description, be sure to use a reliable source for this measurement (barometric altimeter, or a trustworthy map), and specify the source under references.

Coordinates

Coordinates are a convenient way to define a locality that is not only more specific than is otherwise possible with a description, but that is also readily usable in GIS applications. Always include as many decimals of precision as given by the coordinate source. A measurement in decimal degrees given to five decimal places is more precise than a measurement in degrees minutes seconds, and more precise than a measurement in degrees decimal minutes given to three decimal places. Set your GPS to report locations in decimal degrees rather than make a conversion from another coordinate system.

Datum

Except under special circumstances (the poles, for example), coordinates without a datum do not uniquely specify a location. Confusion about the datum can result in positional errors of hundreds of meters. If you are not basing your locality description on a map, set your GPS to report coordinates using the WGS84 datum.

GPS accuracy

Most GPS devices are able to report a theoretical horizontal accuracy based on local conditions at the time of reading. For highly specific localities, it may be possible for the potential error in the GPS reading to be on the same order of magnitude as the extent of the locality. In these cases, the GPS accuracy can make a non-trivial contribution to the overall uncertainty in the position given by the coordinates. By habitually recording the GPS accuracy, you will not have to worry about whether this is the case, and your data will be of the highest possible quality.

Extent

Collecting and observations often take place in an area described collectively by a single locality (e.g., within 1 km of the place described in the recorded locality). Without a measure of the potential deviation from the point provided, a user of the data usually has no way to know how specific the locality actually is. The extent is a simple way to alert the user that, for example, all of the specimens I say I collected at the coordinates I recorded were actually up to 0.5 miles from that point. It can be quite helpful at times to include in your field notes a large-scale map of the local vicinity for each locality, marking the area in which the collecting and observations occurred.

Juran, J.M. 1964. Managerial Breakthrough. New York. McGraw-Hill.


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