Parallels of Latitude Meridians of Longitude Graticular Network Georeferencing Using MaNIS/HerpNET/ORNIS Guidelines.

Parallels ofLatitude

Meridians ofLongitude

GraticularNetwork

Georeferencing Using Georeferencing Using MaNIS/HerpNET/ORNIS MaNIS/HerpNET/ORNIS

GuidelinesGuidelines

Datum(Geodetic)Datum(Geodetic)::Defines the position of Defines the position of the origin, scale, and the origin, scale, and the orientation of the the orientation of the axes of a coordinate axes of a coordinate system. A model of the system. A model of the earth used for geodetic earth used for geodetic calculations.calculations.

Coordinate reference Coordinate reference systemsystem: a coordinate : a coordinate system that relates a system that relates a system of numbers system of numbers (latitude, longitude) to (latitude, longitude) to the real word via a the real word via a datum.datum.

Geographical Concepts:Geographical Concepts:

Map Projections:Map Projections: ProjectionsProjections are are the mathematical the mathematical

transformation of the three-transformation of the three-dimensional surface of the earth dimensional surface of the earth into a flat map sheet, or the into a flat map sheet, or the projection of the 3-D spheroid into projection of the 3-D spheroid into a 2-D map (e.g. conical, cylindrical, a 2-D map (e.g. conical, cylindrical, azimuthal and these types can be azimuthal and these types can be equal area or equidistant).equal area or equidistant).

They all suffer from distortions, They all suffer from distortions, either in area, shape, distance, or either in area, shape, distance, or direction.direction.

When measuring distances on When measuring distances on paper maps, use an equal distant paper maps, use an equal distant projection or equal area if near the projection or equal area if near the central meridian.central meridian.

ExtentExtent:the geographic :the geographic range, magnitude or distance range, magnitude or distance that a location may actually that a location may actually represent. (With a town, the represent. (With a town, the extent is the polygon that extent is the polygon that encompasses the area inside encompasses the area inside the town’s boundaries.)the town’s boundaries.)

Linear extentLinear extent- what we use - what we use for the Point-Radius Method. for the Point-Radius Method. Defined as the distance from Defined as the distance from the geographic center of the the geographic center of the location to the furthest point location to the furthest point of the geographic extent of of the geographic extent of the location.the location.

Extents:Extents:

MaNIS/HerpNET/ORNIS MaNIS/HerpNET/ORNIS Guidelines Guidelines http://http://manisnetmanisnet.org/.org/GeorefGuideGeorefGuide

.html.html The point-radius method of georeferencingThe point-radius method of georeferencing Uses the coordinate (point) of the center of a place, and an Uses the coordinate (point) of the center of a place, and an

uncertainty (“error”) around it to account for extent of the uncertainty (“error”) around it to account for extent of the named place, uncertainty of direction and distance, datum named place, uncertainty of direction and distance, datum used, etc.used, etc.

We assume that the point and radius will contain the actual We assume that the point and radius will contain the actual collection localitycollection locality

Purpose behind these methods is to provide assumptions Purpose behind these methods is to provide assumptions that will produce consistent results that can be replicatedthat will produce consistent results that can be replicated

If more information is known about a locality and the If more information is known about a locality and the georeferencer wants to use this information, then state any georeferencer wants to use this information, then state any assumptions made in the “LatLong Remarks”.assumptions made in the “LatLong Remarks”.

Named PlaceNamed Place – –

Used to refer to traditional and Used to refer to traditional and non-traditional features (towns, non-traditional features (towns, cities, mountains, ranches, cities, mountains, ranches, highway mile markers, highway mile markers, townships). We take the extent of townships). We take the extent of the named place.the named place.

Named Place - Urban AreaNamed Place - Urban Area

Locality consists of a reference to Locality consists of a reference to a geographical feature having a a geographical feature having a spatial extent, example is “Las spatial extent, example is “Las Vegas, Nevada”Vegas, Nevada”

Types of Localities:Types of Localities:

If the geographic center does not fall within the If the geographic center does not fall within the shaded urban area, choose the nearest point shaded urban area, choose the nearest point to the center within the shape.to the center within the shape.

Named Place – Street AddressNamed Place – Street Address

““#10 Downing St., London, England”#10 Downing St., London, England”

Extent is the smallest area possible that cannot be mistaken Extent is the smallest area possible that cannot be mistaken for another address, sometimes ½ a city block.for another address, sometimes ½ a city block.

Locality Types:Locality Types:

Named Place – RemoteNamed Place – Remote

A locality that does not have a clear boundary on the mapA locality that does not have a clear boundary on the map

““Amargosa Valley (town), NV”Amargosa Valley (town), NV”Extent is half the distance to the center of the nearest named place Extent is half the distance to the center of the nearest named place (or feature).(or feature).

Locality Types:Locality Types:

Locality Types:Locality Types: Named PlaceNamed Place – Lake, – Lake,

Mountain, Cultural Land, Mountain, Cultural Land, or Other Geographic Entityor Other Geographic Entity

““Mount Vesuvius, Italy”Mount Vesuvius, Italy”

Extent is usually half the length Extent is usually half the length from the coordinates of the from the coordinates of the center of the named place to the center of the named place to the furthest point within the named furthest point within the named place.place.

Distance from a Distance from a named place using the named place using the location of the named location of the named place as a starting place as a starting point. Used with a point. Used with a heading to give heading to give direction and distance direction and distance from named place.from named place.

These can be in a These can be in a direction, direction and direction, direction and distance, direction distance, direction along a path, etc.along a path, etc.

Offsets:Offsets:

““5 miles north of Beatty, on US 95”5 miles north of Beatty, on US 95”

Maximum Error Distance from Uncertainties:Maximum Error Distance from Uncertainties:Defined as the numerical value for the upper limit of the distance from the 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 coordinates of a locality to the outer extremity of the area within which the whole of the described locality must lie whole of the described locality must lie ((i.ei.e., what can be mistaken for that ., what can be mistaken for that locality based on the description given).locality based on the description given).

Causes of uncertainty:Causes of uncertainty:

Map scaleMap scale

The extent of the localityThe extent of the locality

GPS accuracyGPS accuracy

Unknown datum (results in Unknown datum (results in >100 m >100 m

Imprecision in distance Imprecision in distance measurementsmeasurements

Imprecision in direction Imprecision in direction measurementsmeasurements

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  1:100,00

0167 ft 50.9 m

1:250,000 417 ft 127 m

Georeferencing Error CalculatorGeoreferencing Error Calculator

Precision and Accuracy:Precision and Accuracy:

Always use as many decimal places as given by the Always use as many decimal places as given by the coordinate source.coordinate source.

A measurement in decimal degrees give to five decimal A measurement in decimal degrees give to five decimal places is more precise than a measurement in degrees places is more precise than a measurement in degrees minutes seconds.minutes seconds.

False precisionFalse precision will result if data are recorded with a will result if data are recorded with a greater number of decimal points.greater number of decimal points.

Always record the Always record the accuracy of your GPS readingsaccuracy of your GPS readings (how (how well the GPS measures the true value of the location). The well the GPS measures the true value of the location). The accuracy is given at the same time as the coordinate but accuracy is given at the same time as the coordinate but usually will not be recorded with the coordinates on most usually will not be recorded with the coordinates on most GPS units.GPS units.

Acknowledgements:Acknowledgements:

MaNIS/HerpNET/ORNIS MaNIS/HerpNET/ORNIS Georeferencing GuidelinesGeoreferencing Guidelines

Guide to Best Practices in Guide to Best Practices in Georeferencing (draft) edited by Georeferencing (draft) edited by Arthur Chapman, BioGeomancerArthur Chapman, BioGeomancer

The point radius method for The point radius method for georeferencing locality descriptions georeferencing locality descriptions and calculating associated and calculating associated uncertainty by John Wieczorek, et uncertainty by John Wieczorek, et al., 2004. Available at (#9) al., 2004. Available at (#9) http://herpnet.org/documents.htmlhttp://herpnet.org/documents.html

Figures from MHO Guidelines, Figures from MHO Guidelines, Terrain Navigator, Geographer’s Terrain Navigator, Geographer’s Craft and Carla CiceroCraft and Carla Cicero