Clarify which ISRM was used for CARB report

## Question for the UW team:

Q. Which ISRM was used to generate the results in the CARB [report][apte2019method]? Was it:

a. [The contiguous-US ISRM hosted on Zenodo][Zenodo]; or
b. [The California-specific ISRM shared via Google Drive][GDrive] ?

The former ISRM has 51k cells, ~9k of which are “California”. We’ve received polygons corresponding to that ISRM for the whole US, and that’s great. The former is also the basis for the iF calculations in issue #1.

The latter ISRM has 21k cells. I'm not sure we’ve received corresponding geometries for it (?) The latter also seems to be the basis for the CARB report; p. 11 says there are 21k "emission locations."

And, if I map the Bay Area based on the polygons we've received to date (i.e., those for the contiguous-US ISRM), it seems like the map is not quite right. Compare, for example, the same areas (circled in red) on the two maps below. The smallest cells are always ~1 km², but it seems like there are more cells in the CARB-report map. So it's not really "higher-res" — but there are more 1 km² cells.

### Map based on polygons received (as of 2022-04-22):


### Map found in CARB report (p. 11)


## Related Issues

- #1
- #3

[apte2019method]: ../blob/master/References/Literature/PDF/apte2019method.pdf
[Zenodo]: https://zenodo.org/record/2589760#.YgREvS2ZPEa
[GDrive]: https://drive.google.com/drive/folders/1WmLRz7iWo2MjtSikgHEig7M0NvK2sOns?usp=sharing

[ca_isrm_gridcells.csv]: ../blob/40da61d/Data/UW/2022-02-10/ca_isrm_gridcells.csv

[CMAQ boundary]: ../blob/40da61d/Build/RData/

Start by comparing page 11 of References/Literature/PDF/apte2019method.pdf with the contiguous-US ISRM on Zenodo and the California-specific ISRM in Google Drive. Review related issues #1 and #3, then confirm which ISRM generated the CARB results and whether matching geometries are available.

Written by the indexing model from the issue text.