Meridians of Graticular Parallels of Latitude Longitude Network Georeferencing Using MaNIS/HerpNET/ORNIS Guidelines & How To Write Localities
Geographical Concepts: • Datum(Geodetic): Defines the position of the origin, scale, and the orientation of the axes of a coordinate system. A model of the earth used for geodetic calculations. • Coordinate reference system: a coordinate system that relates a system of numbers (latitude, longitude) to the real word via a datum.
Map Projections: • Projections are the mathematical transformation of the three-dimensional surface of the earth into a flat map sheet, or the projection of the 3-D spheroid into a 2-D map (e.g. conical, cylindrical, azimuthal and these types can be equal area or equidistant). • They all suffer from distortions, either in area, shape, distance, or direction. • When measuring distances on paper maps, use an equal distant projection or equal area if near the central meridian.
Extents: • Extent- the geographic range, magnitude or distance that a location may actually represent. (With a town, the extent is the polygon that encompasses the area inside the town’s boundaries.) • Linear extent- what we use for the Point-Radius Method. Defined as the distance from the geographic center of the location to the furthest point of the geographic extent of the location.
MaNIS/HerpNET/ORNIS (MHO) Guidelineshttp://manisnet.org/GeorefGuide.html • The “point-radius” method of georeferencing • Uses the coordinate (point) of the center of a place, and an uncertainty (“error”) around it to account for extent of the named place, uncertainty of direction and distance, datum used, etc. • We assume that the point and radius will contain the actual collection locality • Purpose behind these methods is to provide assumptions that will produce consistent results that can be replicated, to enhance the value of specimen collections, and to design a “paradigm that could be easily adopted by other disciplines with similar needs.”
Data Quality • “Fitness of use” of the data • As a collector, you may have an intended use for the data you collect but data you collect but data have the potential to be used in unforeseen ways…. The value of your data is directly related to the fitness for a variety of uses. • As data become more accessible many more uses become apparent. – Chapman 2005, Chapman and Wieczorek 2006 • We are using the MHO methods as a tool to enhance data quality
Maximum Error Distance from Uncertainties: • Uncertainty is a “measure of the incompleteness of ones knowledge or information about an unknown quantity whose true value can be established if a perfect measure device were available.” (Cullen & Frey 1999) • In MHO Guidelines, this is defined as the numerical value for the upper limit of the distance from the coordinates of a locality to the outer extremity of the area within which the whole of the described locality must lie (i.e., what can be mistaken for that locality based on the description given).
Scale Uncertainty (ft) Uncertainty (m) 1:1200 3.3 ft 1.0 m 1:2400 6.7 ft 2.0 m 1:4800 13.3 ft 4.1 m 1:10,000 27.8 ft 8.5 m 1:12,000 33.3 ft 10.2 m 1:24,000 40.0 ft 12.2 m 1:25,000 41.8 ft 12.8 m 1:63,360 106 ft 32.2 m 1:100,000 167 ft 50.9 m 1:250,000 417 ft 127 m Causes of uncertainty: • Map scale • The extent of the locality • GPS accuracy (assume 30 m since Selective Availability ended 2 May 2000, previously >=100 m error) • Unknown datum • Imprecision in distance measurements (1 mile, instead of 1.1 mile) • Imprecision in direction measurements
Precision and Accuracy: • Always use as many decimal places as given by the coordinate source. • A measurement in decimal degrees give to five decimal places is more precise than a measurement in degrees minutes seconds. • False precision will result if data are recorded with a greater number of decimal points (e.g. when converting from DMS to decimal degrees). • Always record the accuracy of your GPS readings (how well the GPS measures the true value of the location). The accuracy is given at the same time as the coordinate, but usually will not be recorded with the coordinates when you output them on most GPS units. Otherwise we assume 30 m of accuracy, so stating your accuracy is better.
Locality Types: • Named Place – Used to refer to traditional and non-traditional features (towns, cities, mountains, ranches, highway mile markers, townships). We take the extent of the named place. • Jean, Nevada(using USGS – Terrain Navigator)
Offsets: • Distance from a named place using the location of the named place as a starting point. Used with a heading to give direction and distance from named place. • These can be in a direction, direction and distance, direction along a path, etc. “5 miles north of Beatty, on US 95”
Locality Types: Offsets by road Locality Types: Offsets using 2 cardinal directions by air • error is smaller for both than one direction by • air (4.692 miles)
How To Take Good Locality Data(i.e., how to describe a locality with the lowest possible error): • The best localities are descriptions: • 1) a distance and heading along a path from a nearby and well-defined intersection • Or, 2) two cardinal offset distances by air (N,S,E,W) from a single nearby feature of small extent • These types of descriptions will decrease the extent and error of your description. Remember, descriptions are still used, even when a GPS was used, to find a locality. Especially if you write the GPS incorrectly, or do not collect right where the GPS was taken.
Other GPS/Coordinate facts: • Use decimal degrees, N and E hemispheres are positive, W and S are negative (e.g., 32.000, -112.564 is in the northern and western hemisphere) • Report the datum from your GPS (standard is WGS84) • Report the accuracy from your GPS • Report an extent from the place that the GPS was taken (e.g., diameter of 1 mile from the car, for trap lines, take GPS from the center) • Use barometric altimeter instead of GPS for altitude • Report what kind of GPS unit you use for lat/longs, also any map reference, source for elevation data
How to take localities at MVZ: • Written from the specific to the general: • Underline the locality with a wavy line, with the date to the left of the margin:
Example of Bad Localities • Vague Localities: Example: Pond along Chattahoochee River, Fulton Co., GA (there are 100s of ponds along the river, state a specific place that the pond is 2 cardinal directions from) • Names of roads without additional references: If traveling along a road, state that, along with the name of the road. If traveling by air, state that. Give an exact place you are traveling from, otherwise we will assume a large extent for the named place (we start in the center of a place). • Localities that are difficult to differentiate: - For many countries, especially Latin America, there are many cities with the same name in any province. State which city by naming distances from other places to differentiate the choices. - When there are several places (mountain, lake, city, river) near each other with the same name, identify which one you are referring to: e.g., South Lake Tahoe (city), California
Things To Watch Out For: -When there are several places (mountain, lake, city, river) near each other with the same name, identify which one you are referring to: e.g., South Lake Tahoe (city), California. -When crossing state/county lines, make sure you say which county/state the start and end places are located, e.g., 2.5 mi north on Highway 80 of Rodeo (New Mexico), Cochise County, Arizona, US -Make sure to spell the name of the place correctly (misspelled names can be misinterpreted) - Specify distances as exact as possible (to the nearest 0.1 of a mile or kilometer, instead of just to nearest mile) -