What is spatially and chemically heterogeneous materials?

Follow this paper,

[Structural analysis of humins formed in the Brønsted acid catalyzed dehydration of fructose](http://pubs.rsc.org/en/Content/ArticleLanding/2018/GC/C7GC03054A#!divAbstract) 


They explained "humins are spatially and chemically heterogeneous materials."


I found "spatial" means "about space" but I think this meaning doesn't correlate with this context"


In summary,
What is spatially and chemically heterogeneous materials? and How did they know humins are spatially and chemically heterogeneous materials?




*Spatially heterogeneous* means that the composition varies as a function of position within the material (varies "in space").


*Chemically heterogeneous* means that the chemical composition just varies in general. In this case, I assume they desire to emphasize that the composition varies among species of widely differing molecular weights—from large polymers down to small molecules.


So, it appears to me that "*spatially and chemically heterogeneous*" was used to emphasize that the chemical composition varies significantly, in particular as compared to prior assumptions; and that this compositional variability *itself* varies as a function of position within a given volume of the material.




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In general, "spatially and chemically heterogeneous" would be rather a redundant term: a material can't really be *spatially heterogeneous* without also being *chemically heterogeneous*: if a substance is chemically pure, there is no possibility of any spatial distribution of compositional variations. So, I think the particular history of this material, which apparently had been assumed to consist only of polymeric material, is what led the authors to use the phrase.


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