Georeferencing Quick Reference Guide

The locality type refers to the pattern of the most specific part of a locality description to be georeferenced – the one that determines which calculation method to use. The Calculator has options to compute georeferences for six basic locality types:

Selecting a locality type will configure the Calculator to show all of the parameters that need to be set to perform the georeference calculation. This Guide gives specific instructions for how to set the parameters for many different examples of each of the locality types.

The corrected center is the point within a location, or on its boundary, that minimizes the geographic radial (see §1.6.3). This point is obtained by finding the smallest enclosing circle that contains the entire feature, and then taking the center of that circle (Figure 1A). If that center does not fall on or inside the boundaries of the feature, find the smallest enclosing circle that contains the entire feature, but has its center on the boundary of the feature (Figure 1B). Note that in the corrected case, the new circle, and hence the radial, will always be larger than the uncorrected one. In the Calculator, the coordinates corresponding to the corrected center are labelled as Input Latitude and Input Longitude. See Appendix B: Methods to Find the Corrected Center and Geographic Radial for techniques to determine the corrected center.

A feature is a place in the locality description that has an extent and can be delimited by a boundary. The geographic radial of the feature (shown as Radial of Feature in the Calculator) is the distance from the corrected center of the feature to the furthest point on the geographic boundary of that feature (see Figure 1 and Extent of a Location in Georeferencing Best Practices (Chapman & Wieczorek 2020)). Note that the radial was called "extent" in earlier documents and versions of the Calculator. See Appendix B: Methods to Find the Corrected Center and Geographic Radial for techniques to determine the geographic radial.

Labelled as Input Latitude in the Calculator. The geographic coordinate north or south of the equator (where latitude is 0) that represents the starting point for a georeference calculation and depends on the locality type.

Latitudes in decimal degrees north of the equator are positive by convention, while latitudes to the south are negative. The Calculator supports three degree-based geographic coordinate formats for latitude and longitude: decimal degrees (e.g. −41.0570673), degrees decimal minutes (e.g. 41° 3.424") and degrees minutes and seconds (e.g. 41° 3' 25.44" S).

Labelled as Input Longitude in the Calculator. The geographic coordinate east or west of the prime meridian (an arc between the north and south poles where longitude is 0) that represents the starting point for a georeference calculation and depends on the locality type.

Longitudes in decimal degrees east of the prime meridian are positive by convention, while longitudes to the west are negative. The Calculator supports three degree-based geographic coordinate formats for latitude and longitude: decimal degrees (−71.5246934), degrees decimal minutes (71° 31.482") and degrees minutes and seconds (71° 31' 28.90" W).

The Coordinate Source is the type of resource (map type, GPS, gazetteer, locality description) from which the starting Input Latitude and Longitude were derived.

This term is related to, but NOT the same as, the Darwin Core term georeferenceSources, which requires the specific resources used rather than their type. Note that the uncertainties from the two sources gazetteer and locality description can not be anticipated universally, and therefore do not contribute to the global uncertainty in the calculations. If the error characteristics of these sources are known, they can be added in the Measurement Error field before calculating. If the source GPS is selected, the label for Measurement Error will change to GPS Accuracy, which is where the accuracy of the GPS (see Using a GPS in Georeferencing Best Practices (Chapman & Wieczorek 2020)) at the time the coordinates were taken should be entered.

The Coordinate Format in the Calculator defines the representation of the original geographic coordinates (decimal degrees, degrees minutes and seconds (DMS) or degrees decimal minutes) of the coordinate source.

This term is only equivalent to the Darwin Core term verbatimCoordinateSystem if no conversions had to be performed from the original source to the format used in the Input Latitude and Input Longitude (e.g. if the original coordinates were UTM and you had to convert them to DMS, then the Coordinate Format in the Calculator will be DMS, but the verbatimCoordinateSystem will be UTM. Selecting the original coordinate format allows the coordinates to be entered in their native format and forces the Calculator to present appropriate options for coordinate precision. Changing the coordinate format will automatically reset the coordinate precision value to nearest degree. Be sure to correct this for the actual coordinate precision. The Calculator stores coordinates in decimal degrees to seven decimal places. This is to preserve the correct coordinates in all formats regardless of how many coordinate transformations are done.

Labelled in the Calculator as Precision in the first column of input parameters, this drop-down list is populated with levels of precision in keeping with the coordinate format chosen. For example, with a Coordinate Format of degrees minutes seconds, an Input Latitude of 35° 22' 24" N and an Input Longitude of 105° 22' 28" W, the Coordinate Precision would be nearest second. A value of exact is any level of precision higher than the otherwise highest precision given on the list. Sources of coordinate precision may include paper or digital maps, digital imagery, GPS, gazetteers, or locality descriptions.

Defines the position of the origin and orientation of an ellipsoid upon which the coordinates are based for the given Input Latitude and Longitude (see coordinate reference system).

The term Datum in the Calculator is equivalent to the Darwin Core term geodeticDatum. The Calculator includes ellipsoids on the Datum drop-down list, as sometimes that is all that coordinate source shows. The choice of datum in the Calculator has two important effects. The first is the contribution to uncertainty if the datum of the input coordinates is not known. If the datum and ellipsoid are not known, datum not recorded must be selected. Uncertainty due to an unknown datum can be severe and varies geographically in a complex way, with a worst-case contribution of 5359 m (see Coordinate Reference System in Georeferencing Best Practices (Chapman & Wieczorek 2020)). The second important effect of the datum selection is to provide the characteristics of the ellipsoid model of the earth, on which the distance calculations depend.

The Direction in the Georeferencing Calculator is the heading given in the locality description, either as a standard compass point (see Boxing the compass) or as a number of degrees in the clockwise direction from north. True North is not the same as Magnetic North (see Headings in Georeferencing Best Practices (Chapman & Wieczorek 2020)). If a heading is known to be a magnetic heading, it will have to be converted into a true heading (see NOAA’s Magnetic Field Calculator) before it can be used in the Calculator. If degrees from N is selected, a text box will appear to the right of the selection, into which the degree heading should be entered.

The Offset Distance in the Calculator is the linear surface distance from a point of origin. Offsets are used for the Locality Types Distance at a heading and Distance only. If the Locality Type Distance along orthogonal directions is selected, there are two distinct offsets:

The Distance Units selection denotes the real world units used in the locality description. It is important to select the original units as given in the description. This is needed to incorporate the uncertainty from Distance Precision properly. If the locality description does not include distance units, use the distance units of the map from which measurements are derived.

The Distance Precision, labelled in the Calculator as Precision in the second column of input parameters, refers to the precision with which a distance was described in a locality (see Uncertainty Related to Offset Precision in Georeferencing Best Practices (Chapman & Wieczorek 2020)). This drop-down list is populated based on the Distance Units chosen and contains powers of ten and simple fractions to indicate the precision demonstrated in the verbatim original offset.

The Measurement Error accounts for error associated with the ability to distinguish one point from another using any measuring tool, such as rulers on paper maps or the measuring tools on Google Maps or Google Earth. The units of measurement must be the same as those in the locality description as captured in Distance Units (see §1.6.12). The Distance Converter at the bottom of the Calculator is provided to aid in changing a measurement to the locality description units. For example, a reasonable value for measurement error on a map is 1 mm, which on a map of 1:24,000 scale would be 24 m.

When GPS is selected from the Coordinate Source drop-down list, the label for the Measurement Error text box changes to GPS Accuracy. We recommend entering a value that is at least twice the value given by the GPS at the time the coordinates were captured (see Uncertainty due to GPS in Georeferencing Best Practices (Chapman & Wieczorek 2020). If GPS Accuracy is not known, enter 100 m for standard hand-held GPS coordinates taken before 1 May 2000 when Selective Availability was discontinued. After that, use 30 m as a conservative default value.

The Uncertainty in the Calculator is the calculated result of the combination of all sources of uncertainty (coordinate precision, unknown datum, data source, GPS accuracy, measurement error, feature extent, distance precision and heading precision) expressed as a linear distance – the geographic radial of the georeference and the radius in the point-radius method (Wieczorek et al. 2004). Along with the Output Latitude, Output Longitude, and Datum, the radius defines a circle containing all of the possible places a locality description could mean. In the Calculator the Uncertainty is given in meters.

The locality refers to a geographic feature with discernible spatial extent, i.e. the boundaries of the feature can be determined easily (Figure 2).

Locality Type: Geographic feature only

Step 1 – Determine the feature boundaries: This step is to determine the shape that contains the feature. This is typically done by drawing a polygon around the feature (Figure 2A), but some features may require more complex geometries, such as multiple polygons.

Step 2 – Determine the coordinates: Use the coordinates of the corrected center of the feature ("a" in Figure 2B) as the Input Latitude and Longitude.

Step 3 – Measure the geographic radial: Measure the distance from the corrected center to the furthest point on the boundary of the feature ("b" in Figure 2B) as the Radial of Feature.

Step 4 – Calculate using the following additional parameters in the Georeferencing Calculator: Coordinate Source, Coordinate Format, Datum, Coordinate Precision, GPS Accuracy/Measurement Error, and Distance Units (see §1.6).

The locality refers to a geographic feature that does not have an easily discernible spatial boundary. Some features may have undefined boundaries (e.g. mountains, unincorporated towns, etc.). Other features may only have a label, with no apparent boundaries or size on a map because they are small or obscured on satellite imagery (e.g. spring, monument, etc.). Another possibility is a feature with only coordinates from a gazetteer and no discernible presence on a map.

Locality Type: Geographic feature only

Step 1 – Estimate the feature boundaries: Determine the boundaries of the feature as well as possible using visible evidence for the feature on a map. Try to get into the mind of the person who recorded the locality. Imagine yourself there. What circumstances would influence which feature was recorded and what circumstances would have encouraged them to choose a different feature?

For towns without obvious borders one can use the presence of buildings near the coordinates given for the town to decide where the town ends (Figure 3). In some cases there might not be such indicators and these will be more subjective. For this reason it is particularly important to document the rationale for the selection of the locality with unclear boundaries.

Where there are no indicators for the boundary, use the midpoint between the given feature and neighbouring features with similar type, size, or importance to make a rough boundary. Though this boundary may not represent the actual feature very well, it will represent the uncertainty of where the locality is, and that is the major goal of the georeference.

For small features, where the only indicator on a map is a label and possibly a marker, or where there are only coordinates from a gazetteer (and no further indicators at those coordinates on a map), a good strategy would be to use a predefined default size based on the feature type (Figure 4, Table 1).

† Grids based on geographic coordinates, such as Quarter Degree Squares, are not square, nor are they constant. They vary in size and shape by latitude. See table in Uncertainty Related to Coordinate Precision in Georeferencing Best Practices (Chapman & Wieczorek 2020).

The boundaries between mountains can be determined by using the terrain (valleys, saddles, and plains) that separate one mountain from others around it (Figure 5).

Always use georeferenceRemarks to document the decisions made and the reasons for them as well as possible, including the neighbouring features used for reference.

Step 2 – Determine the coordinates: Once the estimated boundary has been determined, use the coordinates of the corrected center (Figure 2, Figure 3, and Figure 5B) as the Input Latitude and Longitude.

Step 3 – Measure the geographic radial: Once the rough boundary and the coordinates of the corrected center have been determined, find the geographic radial as the Radial of Feature by measuring the distance from the corrected center to the furthest point on the estimated boundary of the feature.

Step 4 – Calculate using the following additional parameters in the Georeferencing Calculator: Coordinate Source, Coordinate Format, Datum, Coordinate Precision, GPS Accuracy/Measurement Error, Distance Units (see §1.6).

The following are special cases of features that might or might not have an obvious spatial extent, depending on the completeness of the information available.

Locality consists of an offset from a feature without any direction specified.

Locality Type: Distance only

Step 1 – Determine the feature boundaries: Determine the boundary of the feature as you would for §2.1.3.8, except that the distance to use for the buffer is the distance given in the locality description, and there is no need to account for the proximity of other features.

Step 2 – Determine the coordinates and geographic radial: Once the boundary has been determined, obtain the coordinates and the geographic radial as for §2.1.1, namely, measure the distance from the coordinates of the corrected center to the furthest point on the boundary of the feature.

Offset Distance: Set to 0. The distance has already been incorporated in the determination of the boundary. Use the distance and units given in the locality description to georeference using the Georeferencing Calculator.

Distance Precision: Though the Offset Distance is set to zero, the Distance Precision should still be set (see §1.6.13) to account for this source of uncertainty.

Step 3 – Calculate using the following additional parameters in the Georeferencing Calculator: Coordinate source, Coordinate Format, Datum, Coordinate Precision, Measurement Error (see §1.6).

The locality consists of a direction from a feature without any distance specified. Note that seldom is such information given alone; there is usually some supporting information. For example, the locality may have higher-level geographic information such as "East of Albuquerque, Bernalillo County, New Mexico". This provides a stopping point (the county border), and should allow you to georeference the locality. Alternatively, there might be another similar feature in the direction of the given heading that can constrain the offset.

Locality Type: Geographic feature only

Step 1 – Determine the feature boundaries: First determine the boundary of the given feature based on the feature type, either as for §2.1.1, or as for §2.1.2. Then, to account for the offset at a heading, extend that boundary outward in a cone defined by the heading uncertainty (see Offset – Direction Only and Uncertainty Related to Heading in Georeferencing Best Practices (Chapman & Wieczorek 2020)) until reaching a constraining boundary imposed by other information in the locality record, or until reaching the proximity of another similar feature, whichever is nearer to the original feature (Figure 17A). Call this the "extended feature". If the extension impinges on any similar extension of another similar feature in the cone of the specified heading, modify the boundary in the shared space to be half the distance between the nearest boundaries between the two features (Figure 17B). For example, "N Palmetto" could mean "northern part of Palmetto" or "North of Palmetto". Since we have no way of knowing which was intended, we choose the latter interpretation, which is more inclusive and will entirely contain the less inclusive interpretation. Use the rules for heading uncertainty to determine the angle within which to find the nearest similar feature. For example, for "N Palmetto" look for a named place somewhere between NE and NW of Palmetto.

Step 2 – Determine the coordinates and geographic radial: Once you have determined the boundary of the extended feature, treat as for §2.1.1, namely, measure the distance from the coordinates of the corrected center to the furthest point on the boundary of the extended feature.

Step 3 – Calculate using the following additional parameters in the Georeferencing Calculator: Coordinate Source, Coordinate Format, Datum, Coordinate Precision, GPS Accuracy/Measurement Error, Distance Units (see §1.6).

The locality consists of a reference feature to start from and a distance to travel along a path from there. Most of the time there will be just one path that matches the description and it will not be very wide compared to the reference feature, for example, a highway out of a town, or a stream out of a lake. In cases such as these, the georeferencing method is relatively simple (see §2.2.3.1). If the path is wide enough that multiple possible routes could be taken along it, such as in a wide river, the method for dealing with it is a little more complex (see §2.2.3.2). Sometimes there might be multiple distinct possible paths that match the locality description, such as two different roads in the same general matching direction out of a town, and there is a third method to use to find the georeference (see §2.2.3.3). In all cases, the georeference will cover a segment of the path or possible paths that includes all the sources of uncertainty. Though there might be a heading mentioned in the locality description (e.g. "9 km S El Bolsón on Ruta 40"), it serves only to constrain which path or paths are possible, and does not contribute uncertainty due to heading precision.

First let’s get an idea of how large the elevation effect can be, to understand the circumstances under which it is worth making the extra effort to estimate the distance on the ground. An important thing to understand is that the changes in elevation, both up and down, contribute to lengthen the route relative to the horizontal distance. The distance on the ground, on the path, is \$sqrt(x^2+y^2)\$, where \$x\$ is the projected horizontal distance and \$y\$ is the accumulated sum of changes in elevation. Note that the accumulated sum of changes in elevation is not necessarily the same as the final change in elevation between the starting point and the ending point of the trajectory. On a road, there could be ups and downs, and the sum of changes includes both, added as absolute values.

Let’s take an extreme case using the steepest road in the world, Baldwin Street in Dunedin, New Zealand. The street has a maximum grade of 35%. For comparison, highways with grades of 6% are usually considered steep enough to merit cautionary signage, and more than about 12% is rare to find. With a 35% grade, \$y\$ is 0.35 times \$x\$. Set \$x = 1\$ and do the calculation. The distance on the ground would be \$sqrt(0.35^2 + 1^2)\$ or 1.059 (5.9% longer). In a more normal extreme case of a 10% grade, the difference would be just 0.5%. Thus, under normal circumstances the difference is essentially negligible for roads and certainly so for navigable waters.

There are several ways to estimate distances on the ground without specialized tools or GIS. One way is to use an image of the elevation profile, which can be obtained using a screen capture in Google Earth Pro, for example. The image must be distorted so that the scale in both \$x\$ and \$y\$ is the same (1m elevation = 1m horizontal distance). With the image thus flattened, measure along the path of elevation and compare it to the length of the horizontal distance on the image.

A second way to estimate the distance on the ground is to sum all the elevation gains between pair-wise minima and maxima and do the same for all the pair-wise elevation losses. Sum the gains and losses (both as positive, because the rises and falls both contribute to positive length gains). Use that sum as the rise (\$y\$) in a slope calculation where the run (\$x\$) is the horizontal length of the path. From \$x\$ and \$y\$, calculate the distance on the ground as above.

A third way to estimate the distance on the ground is a gross simplification of the second method, above. Instead of measuring all pair-wise gains and losses, sum the net changes in elevation along three segments, 1) from the elevation at the beginning of the path to the lowest elevation, 2) the net change from the lowest elevation to the highest elevation, and 3) the net change from the highest elevation to the elevation at the end of the path.

The locality consists of a linear distance in each of two orthogonal directions from a feature. For more information and details see Offset along Orthogonal Directions in Georeferencing Best Practices (Chapman & Wieczorek 2020).

Locality Type: Distance along orthogonal directions

Step 1 – Determine the starting feature boundaries: Determine the boundary of the feature based on whatever the feature type is, either as for §2.1.1, or as for §2.1.2.

Step 2 – Determine the starting feature coordinates and geographic radial: Once the boundary of the starting feature has been determined, use the same method to determine the corrected center and geographic radial as for §2.1.1, namely, measure the distance from the coordinates of the corrected center to the furthest point on the boundary of the starting feature (Figure 21).

Step 3 – Calculate using the following additional parameters in the Georeferencing Calculator: Coordinate Source, Coordinate Format, Datum, Coordinate Precision, North or South Offset Distance, East or West Offset Distance, GPS Accuracy/Measurement Error, Distance Units, Distance Precision (see §1.6).

The locality consists of a distance in a given direction from a single feature. Such localities sometimes contain an explicit indicator of how the distance was measured, (e.g. "by air", "air miles W of", "due N of", "as the crow flies", "by road", "downstream from", etc.). Without such an indicator the interpretation is a matter of judgement, which should be documented in georeferenceRemarks.

Locality Type: Distance at a heading

Step 1 – Determine the starting feature boundaries: Determine the boundary of the feature based on whatever the feature type is, either as for §2.1.1, or as for §2.1.2.

Step 2 – Determine the starting feature coordinates and geographic radial: Once the boundary has been determined, obtain the coordinates and the geographic radial as for §2.1.1, namely, measure the distance from the coordinates of the corrected center to the furthest point on the boundary of the feature.

Step 3 – Calculate using the following additional parameters in the Georeferencing Calculator: Coordinate Source, Coordinate Format, Datum, Coordinate Precision, Direction, Offset Distance, GPS Accuracy/Measurement Error, Distance Units, Distance Precision (see §1.6).

The locality consists of orthogonal offset distances, one from each of two distinct paths.

Locality Type: Distance along path

Although this is not technically a distance along a path, the choice of this locality type in the Georeferencing Calculator will allow all of the relevant parameters to be entered.

Step 1 – Determine the feature boundaries: Determine the boundaries of the area matching the locality description by "transporting" each path by its given offset distance and direction. The transported paths will then overlap, each one having its corresponding buffer due to distance precision and path widths around it. This overlap of the two buffered areas defines the extent of the place described (Figure 22). Draw the boundary around the overlapping area.

Step 2 – Determine the coordinates and geographic radial: Once the boundary has been determined, obtain the coordinates and the geographic radial as for §2.1.1, namely, measure the distance from the coordinates of the corrected center to the furthest point on the boundary of the feature.

Step 3 – Calculate using the following additional parameters in the Georeferencing Calculator: Coordinate Source, Coordinate Format, Datum, Coordinate Precision, Radial of Feature, Measurement Error, Distance Units, Distance Precision (see §1.6).

The locality consists of a point represented by latitude and longitude coordinates in one of various coordinate formats:

Records should also contain a hemisphere indicator ('E' or 'W' and 'N' or 'S' for DMS and DDM formats in English; '−' for west or south in DD format). For maritime locations, if there is no information that would suggest a particular Coordinate Source, use a map of 1:150000 scale, as this is a realistic conservative selection.

Locality Type: Coordinates only

Step 1 – Enter the coordinates: Enter the coordinates in the format they were captured from the GPS or from the verbatim locality (decimal degrees, degrees decimal minutes, or degrees minutes seconds) with all of the given digits of precision.

Step 2 – Calculate using the following additional parameters in the Georeferencing Calculator: Coordinate Source, Datum, Coordinate Precision, GPS Accuracy, Distance Units (see §1.6).

The locality consists of a point represented by coordinate information in the form of Universal Transverse Mercator (UTM) or a related coordinate system. For UTM or equivalent coordinates, a Zone should ALWAYS be included to make sure that the longitude is not ambiguous. Zones are often not reported where a region (e.g. Tasmania) falls completely within one UTM zone. Be aware that UTM zones are valid only between 84°N and 80°S. For details on dealing with UTM Coordinates see Universal Transverse Mercator (UTM) Coordinates in Georeferencing Best Practices (Chapman & Wieczorek 2020).

Locality Type: Geographic feature only

Although this is not technically a feature, the Geographic feature only locality type in the Georeferencing Calculator includes all of the relevant parameters.

Step 1 – Convert the coordinates: The Universal Transverse Mercator UTM coordinates must be converted to decimal degrees using a UTM to Latitude/Longitude conversion tool. If the Zone is not given with the UTM coordinates, try to determine it using UTM Grid Zones of the World (Morton 2006) and any additional geographic information in the locality or geography fields combined with a UTM zone map. Use all of the digits of precision from the conversion in the Input Latitude and Longitude. Choose the Coordinate Source: Locality description

Step 2 – Determine geographic radial: If the UTM coordinates have 7 digits in the northing and 6 digits in the easting, the geographic radial is 0.707 m (because the coordinates distinguish to the nearest meter and the geographic radial is half the diagonal of the 1 m by 1 m grid cell). For UTM coordinates with fewer digits of precision see Table 1. This radial covers the uncertainty from the UTM coordinate precision. The Coordinate Precision in the Calculator for this case is the coordinate precision of the Input Latitude and Longitude, which depends on how many digits of decimal degrees are copied from the converted latitude and longitude (Table 1).

Step 3 – Calculate using the following additional parameters in the Georeferencing Calculator: Coordinate Format, Datum, Coordinate Precision, GPS Accuracy/Measurement Error, and Distance Units (see §1.6).

Locality is a grid reference (see Grids in Georeferencing Best Practices (Chapman & Wieczorek 2020)), such as the 100 m square grids extensively used in Europe, Quarter Degree Square Grids (QDS) as used in South Africa, and the Public Land Survey System (PLSS) system of Townships andSection (TRS) used in the mid- and western USA. Townships in the PLSS system are usually square and six miles on each side, with 36 one-mile by one-mile sections. Be aware that not all townships are square, however, as some were adjusted to conform to administrative or natural boundaries (rivers, for example). Numbered Townships are not unique descriptions without a meridian, which often is not given in a locality description. The meridian must then be inferred from a Principal Meridian map using other information in the locality description. Similar subdivisions are used in other countries, and should be calculated in a similar way, once the sizes of the cells have been determined (see Table 1). Map sheets (quadrangles) are sometimes used and can also be calculated as a grid system. Note that, unlike geographic grids, QDS grids are referenced from the top left corner.

Locality Type: Geographic feature only

Step 1 – Determine the coordinates: Determine as for §2.1.1. Use the coordinates for the corrected center of the named grid cell. Usually a grid is made up of bounding boxes, so determining the corrected center should be easy.

Step 2 – Determine the geographic radial: As for §2.1.1. See Table 1 for radials of regularly shaped Townships, Sections, and subsections.

Step 3 – Calculate using the following additional parameters in the Georeferencing Calculator: Coordinate Source, Coordinate Format, Datum, Coordinate Precision, Measurement Error, and Distance Units (see §1.6).

The most important type of vagueness in a locality description is one in which some or all of the locality is explicitly in question.

Georeferencing procedure: If some part of the locality description is in question, but aside from that there is location information that is not in question, use the unquestioned part of the locality to determine the locality type and georeference it normally following the appropriate method. Document in georeferenceRemarks what had to be disregarded in order to georeference the locality in question. For example, for a locality “Argentina: Misiones, possibly Puerto Iguazú”, georeference “Misiones”, which is the most specific part of the locality that is not in question.

If the entire locality is in question, do not georeference it and document in georeferenceRemarks the reason for not georeferencing (e.g. "locality in question").

The cited locality cannot be found, and there is no other location information in the record (e.g. no administrative divisions cited). This may be for any number of reasons, including:

Do not georeference these localities. These recommendations apply to all locality types. Document in georeferenceRemarks the reason for not georeferencing, e.g. "locality cannot be found with available references". Fill in the georeferenceSources so that others do not waste time using the same resources to track down the locality.

At times the locality cannot be distinguished from among multiple possible candidates because the geographical feature in the locality description has multiple matches.

The locality description contains irreconcilable inconsistencies – assertions that can not all be simultaneously true. Do not georeference these localities. Document in georeferenceRemarks the reason for not georeferencing, e.g. "locality contains irreconcilable inconsistencies".

A common source of inconsistency occurs when the locality description does not match the geopolitical subdivision of which it is supposed to be a part (e.g. "Missoula County, Idaho"). Elevation is another possible source of inconsistency, especially since elevation data are notoriously inaccurate (see Elevation in Georeferencing Best Practices (Chapman & Wieczorek 2020)). It is difficult to know which part of the locality is the one in error and a risk to judge that one part of the description should take precedence over another.

Do not georeference. Rather than determine coordinates for such localities, annotate the locality in georeferenceRemarks with the nature of the inconsistency (e.g. "Missoula County not in Idaho") and refer the locality to the source institution for reconciliation.

The locality is recorded in association with a captive animal, a cultivated plant or some other non-natural occurrence. The locality cited is often that of a zoo, aquarium, botanical garden, etc. (see Dealing with Non-natural Occurrences in Georeferencing Best Practices (Chapman & Wieczorek 2020).

Georeference the locality normally based on the locality type and feature. Retain the location (e.g. zoo) along with its georeference, as for other localities in this Guide, but be sure to record the nature of its provenance (cultivated, captive, washed ashore, etc.) in the Darwin Core term degreeOfEstablishment.