[Enh] Impact of spatial heterogeneity on Spatial Interaction Models

[JusteRaimbault]

Check network based method for spatial heterogeneity of SIM introduced in
Lenka Hasova, Levi John Wolf, 2020, Modelling Urban Flows: Spatial Effects in Origin-Destination data, Proceedings of GISRUK 2020
http://london.gisruk.org/gisruk2020_proceedings/GISRUK2020_paper_74.pdf