An un-conference session saw a lively discussion of the definition of 'sample', exploring if the disciplines represented in the meeting had a shared understanding of the essential characteristics. The concept of 'sampling-feature' from the Observations and Measurements standard (ISO 19156, available as OGC Abstract Specification Topic 20) and Observations Data Model (ODM2) provided a starting point for the definition here.
Thing or subset (real or virtual) which is intended to be representative of a larger thing or set. A sample is created or selected for the purpose of making observations or measurements to determine the value of one or more properties, traits or qualities of the larger thing. The essential property of a sample is the 'is-sample-of' relationship with the larger thing.
A material sample or specimen is typically selected to allow ex-situ observations.
A statistical sample or subset is a specified number of individuals from a population.
A spatio-temporal sample may have the same dimension but a smaller extent than the thing which it represents, or may have a lower topologic dimension than the thing which it represents.
Samples are often related to other samples, either through sub-sampling, or as members of a sequence of siblings, or through specific treatments that transform the original sample into one or more new samples. Sub-sampling may select specific elements of the parent, or may be unbiased. The nature of the relationship is important, but the complete set of relationships cannot be enumerated - this is an important area of innovation in observational protocols.
The identity, or even existence, of the larger thing or population may not be known at sampling time. For example, a material sample or specimen may be collected opportunistically 'because it looks interesting'. However, its scientific significance is only realized if it is determined that it is indeed representative of a larger body or population.
Spatio-temporal samples - lower dimensionality
- Snapshot of a time-varying phenomenon
- Point (0-D sample) within a curve (1-D), surface (2-D) or volume (3-D),
- e.g. monitoring station, pixel
- Curve (1-D) within a surface (2-D) or volume (3-D),
- e.g. transect, flightline, cruise track, borehole trace
- Surface (2-D) within a volume (3-D)
- e.g. cross-section
Spatio-temporal samples - same dimensionality
- interval within a curve
- interval within a time-series
- quadrat within a tract
- core from a body of rock.