Value Ranges

How to capture single / range values using Darwin Core

Biodiversity data often presents attributes that can have single values or ranges of values. Examples of this are dates, where we can have the day in which a collecting event began and the day when it ended; elevations and depths, where we may have ranges of values within which a collecting event took place; or periods in time to which a fossil belongs.

Darwin Core has a series of terms where to capture such ranges, as listed below:

startDayOfYear | endDayOfYear

minimumElevationInMeters│maximumElevationInMeters

minimumDepthInMeters │maximumDepthInMeters

minimumDistanceAboveSurfaceInMeters │maximumDistanceAboveSurfaceInMeters

earliestEonOrLowestEonothem │ latestEonOrHighestEonothem

earliestEraOrLowestErathem │ latestEraOrHighestErathem

earliestPeriodOrLowestSystem │ latestPeriodOrHighestSystem

earliestEpochOrLowestSeries │ latestEpochOrHighestSeries

earliestAgeOrLowestStage │ latestAgeOrHighestStage

lowestBiostratigraphicZone │ highestBiostratigraphicZone

Which field do I use if I only have one value?

Or, in a concrete example, where do I put elevation data if I only have one value, say “300m”? Do I use minimum- or maximumElevationInMeters?

Well, first, if we go to the definitions of these two terms in the Darwin Core standard, we find:

• Maximum Elevation In Meters: The upper limit of the range of elevation (altitude, usually above sea level), in meters.
• Minimum Elevation In Meters: The lower limit of the range of elevation (altitude, usually above sea level), in meters.

Given these definitions, we can answer the following two questions: Which is the maximum elevation I have? Answer: 300m. Which is the minimum elevation I have? Answer: 300m.

Naturally, we would wonder “but, is it OK to fill in both fields with the same value?” And the answer is “Yes”, nothing prevents you from filling up both fields with the same value. Not only that, by doing so, you would be being as specific as you can, not leaving any place for confusion.

This analysis stands for all other pairs of fields which represent upper and lower limits of an attribute, listed above.

For instance, another example would be earliestEpochOrLowestSeries and latestEpochOrHighestSeries in a paleontological record. If our value is “Pliocene”, we would repeat "Pliocene" in both fields.

Having analyzed this as we did, the recommendation would then be:

Recommendation on usage:

For attributes that allow the use of ranges of values, having two fields to capture lower and upper limits of the attribute, if you only have one value, populate both fields with the same value.