In discussions with some collaborators in Japan, it was brought up that there are some issues around having polygon information be openly available. We’ve already been encountering this a little bit with transforming Ottawa data to version 2 of the ODM , and finding it difficult to access and share polygon information.
While polygons for cities aren’t difficult to access/find, polygons for wastewater systems are challenging and sometimes characterized as a national security risk to share. This option (H3) could then address some of these issues by “approximating” the area, being flexible to frequent updates, etc. This could also work well for jurisdictions worldwide that don’t have detailed polygon data.
I have some questions about the implementation of the H3 hexagonal modelling.
Is my understanding correct in that this hexagonal modelling will be used to “blur” the edges of the actual polygons? I see the use in tracing over less detailed polygons/maps/images to have a polygon format used for analysis in collection sites without polygon data.
I was also thinking, do we need to publicly share polygon information? For PHAC’s purposes, the polygons are required to accurately map across surveillance datasets (wastewater, clinical, and other environmental). This could be achieved with internally stored polygons and a spatial join tool.
We discussed this point a bit at the working group meeting last week, but to maintain the records and paper trail I’ll try to capture some discussion here as well.
I think the suggestion was to use the H3 modelling to create “draft” sewersheds where that data is missing, or tracing the low-detailed maps exactly as you suggest!
With regard to the to the open data question, I think on our side we really would like all data to be openly available, including polygons. And when making data public, having information about the area the data covers is useful context and metadata. Though managing it internally is also totally fine.
@Sorin also brought up that he thinks it would be better to use Voronoi Diagrams because they make better approximations of the polygons with fewer data points. Steven also pointed out that the polygons can be very unintuitive, citing the example of Toronto’s three sewersheds.
This issue is more of a tangential one, but still one for us to continue discussion one. I think it’s also clear that access to polygon information and alternative ways to acquire that information will differ between regions and countries. It was brought up that looking at historic wastewater releases may contain sewer shed boundaries, as would the submissions for approval of a WWTP. But this may only work in Canada/Ontario.