We found that part of the problem is that CCDs 58 and 62 do not overlap with the other images (because I was comparing a East-is-left focal plane map to an East-is-right image of the HiTS 2015 dataset). Looking at only the two visits with CCDs 5 and 10 in a slightly different reduction, we see:

• ~913 DiaObjects with 1 DiaSource
• ~79 DiaObjects with 2 DiaSources

Meredith Rawls thinks the ~10% repeat DiaSources despite the ~100% overlap is because most of the sources are image differencing artifacts; we will make plots of number of sources on the sky for each individual visit to test this hypothesis.

With the dataset amended as described in the comments to DM-15142, the statistics are:

• 1066 DiaObjects with 1 DiaSources
• 91 DiaObjects with 2 DiaSources
• 25 DiaObjects with 3 DiaSources

It appears that updating the CI dataset to include more fully overlapping chips solved the majority of the problem. The plot below shows the sources detected on the sky with the three visits in this dataset. Small gray points are DIAObjects with a single DIASource, medium blue points are DIAObjects with two DIASources, and large orange points are DIAObjects with three DIASources.

It is clear from this plot that there are lots of single-source objects being detected near chip edges and corners. This is most likely due to artifacts in the difference imaging template. I suspect if this plot is recreated when DM-14762 is complete, many of the erroneous gray sources will disappear.

Ian Sullivan, would you be willing to review this? The PR is simply to add the notebook used to generate the plot into the ap_pipe-notebooks repo.

Looks good. I would recommend you remove the commented-out cells at the beginning of the notebook (or add a comment explaining why you left them), and add a description of the final plot in a conclusion. That could probably just be the description you left as a comment here.