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In total, if there are N “nearby” geohashes, a total of 2 x (N + 1) hashes will be stored. These can be stored in an unorded unordered list (i.e. there is no need to store any info on which is which).
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Normally, the data points will be ~5 minutes apart. Where data points are missing, and the gaps are more than 5 minutes apart, this does not need to affect the calculation - the same calculation can be performed, and the Exposure Duration may be calculatyed in the same way.
In some rare cases, if a data point right at the end of the Exposure Duration were to be delayed for a long time (e.g. hours), this would result in an overstatded Exposure Duration. That is a characteristic we can live with - we are actively working to reduce the frequency of this kind of occurrence (SAF-257 / SAF-278).
Related Work
In MVP, under MVP1, under SAF-397 / MVP1#17, we will be doing work to reduce the volume of data downloaded by the Mobile App from Same Places.
Specifically under SAF-275 / PLACES-83, we plan to break the HA JSON file into several pieces, so that each 12 hour publication event results in a new file, rather than additions to an existing file.
Safe Paths will download one or more of these files - typically just one, but in the case that Safe Paths was offline for an extended period it could be more than one..
The Safe Places publishing activity & the Safe Paths handling of points of concern will need to accommodate these changes.
This is expected to be handled by SAF-275 and PLACES-83, but with both developments going on in parallel, there is a risk of conflicts, and so the teams should co-ordinate their designs & activity together.