5/ Time for some history.
There have been thematic maps since at least 350 BC, but many linguists agree the first significant linguistic map was Gottfried Hensel’s famous 1741 map showing linguistic variation across Europe in the Lord’s Prayer.
https://en.wikipedia.org/wiki/Synopsis_Universae_Philologiae
6/ Fast forward a century or two, and the atlas experiences its golden age.
The first explicitly named linguistic atlas was Julius Klabroth’s 1823 “Asia Polyglotta: Sprachatlas”, followed by Adriano Balbi’s 1826 “Atlas ethnographique du Globe”.
These atlases differ from modern ones because the data collected is mostly in comparative tables. The table below illustrates this point well, whilst the map magnificently shows isoglosses.