It wasn't at all clear where the data comes from, but after a little digging it looks like volunteers are driving around with homemade devices collecting data.

It wasn't at all clear where the data comes from, but after a little digging it looks like volunteers are driving around with homemade devices collecting data. https://bgeigiezen.safecast.jp/store-2/ https://bgeigiezen.safecast.jp/store-2/ Looks like they might have had apps too, but they have been pulled from the App Store and Play Store?