Street View Download 360 for Mac OS is downloading...

important:

If you get a message like: “Street View Download 360 can't be opened because it is from an unidentified developer.”,
instead of double-clicking it,
right-click the file in Finder and choose Open.

When the DMG opens, again, right-click the app and select open.

Download directly if the download didn't start automatically. Also see all downloads for other OSs.