reorganize density terms

[stevenchong]

It's not clear what the difference is between mass_density_MeasurementType (ECSO:00001198) and volumentric_density_MeasurementType (ECSO:00001199) because they both have the same definition.

[stevenchong]

@mobb and I were discussing this. We found that count density (ECSO:00001160) has a definition for number density, and also a skos:altLabel for number density. This seems to conflict with the wikipedia definition: https://en.wikipedia.org/wiki/Number_density

[mpsaloha]

Hi--

some folks would say that ALL densities are volumetric-- i.e. density is defined as the "amount of something per volume" (where some PHYS/CHEM folks would even argue that the "amount" must be restricted to a "mass"). However, measures of (and use of the term) "density" to refer to "areal density"-- are common, e.g. 200kg of wheat per hectare, or speaking about "population density", etc. So you are correct to discern that these should have separate definitions!

A mass density focuses on what is in the numerator (mass), while volumetric density focuses on the denominator (volume). But many researchers would call the following non-mass-based, non-volume based measurements densities: https://en.wikipedia.org/wiki/List_of_countries_and_dependencies_by_population_density

So I think we should define density as "amount of something per area or volume", and have subclasses of "areal" and "volumetric" densities (that constrain the denominator). Further subclasses within area might constrain the numerator: "mass density", "number density". "Population density" would be a subclass of "number density" as well as "areal density".

...or something along these lines?

Thanks!

cheers, Mark

On Tue, Sep 17, 2019 at 12:29 PM Steven Chong [email protected] wrote:

It's not clear what the difference is between mass_density_MeasurementType (ECSO:00001198) and volumentric_density_MeasurementType (ECSO:00001199) because they both have the same definition.

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[mobb]

IMO, we want to avoid the situation where someone browsing a tree finds all the different connotations of "density" together. That's the problem we have now (and also with units in EML), and the measurement nuances get conflated by the small set of dimensions that are tied to a few specific terms.

this definition says all number_densities are spatial (but might be volumetric, areal, linear) https://en.wikipedia.org/wiki/Number_density and suggests they have a lot in common with concentrations

[mobb]

Also, I disagree that they are all "volumetric", I think they are all "spatial"