Historical
25 maps that explain the English language
Suzanne Kemmer, 'Maps: Visual Aids for the History of England and English'
Raymond Hickey, 'Maps for the Old English period' 'Maps for the Middle English period', 'Maps for the Early Modern English period'
An Electronic Version of A Linguistic Atlas of Late Medieval English (eLALME) [a revised electronic version of the print volumes published in 1986]
A Linguistic Atlas of Early Middle English (LAEME) 1150 to 1325 [Version 3.2 is now released.]
A Parsed Linguistic Atlas of Early Middle English (PLAEME)
A Linguistic Atlas of Older Scots (LAOS), Phase 1, 1380 to 1500
MoEML - The Map of Early Modern London ['plot people, historical documents, literary works, and recent critical research onto topography and the built environment']
World Englishes
Bert Vaux and Marius L. Jøhndal, Cambridge Online Survey of World Englishes
Kendra Slayton et al., 'Mapping World Englishes' ['includes information about many of the English-based varieties (dialects, creoles, and pidgins) found across the globe']
UK
Adrian Leemann, English Dialect App [By answering a set of questions, your 'broader dialect region' is localised on a map of England.]
Laurel MacKenzie et al., 'Our Dialects - Mapping variation in English in the UK' [maps of linguistic diversity based on student-run questionnaires]
Jennifer Smith et al., Scots Syntax Atlas ['The Scots Syntax Atlas presents the results of over 100,000+ acceptability judgments from over 500 speakers on over 250 morphosyntactic phenomena. The Atlas also contains a text-to-sound aligned corpus of spoken data totalling 275 hours and over 3 million words.']
Literary Atlas: Plotting English Language Novels in Wales ['an interactive online atlas of digital deep maps of twelve English-language novels set in Wales']
North America
Linguistic Atlas Project Online ['a set of survey research projects about the words and pronunciation of everyday American English, the largest project of its kind in the country']
Rick Aschmann, 'North American English Dialects, Based on Pronunciation Patterns' [see the review of this page here]
Telsur Project: Phonological Atlas of North America
Bert Vaux, Harvard Dialect Survey [note that the page is no longer actively maintained]
Sandra Clark et al., DANL (The Online Dialect Atlas of Newfoundland and Labrador English) [an online interactive dialect atlas is being prepared]
Jack Chambers, Atlas of Dialect Topography ['a research project that investigates what English words people use in Canada, as well as regions of the United States that border Canada']
Others
Diachronic Atlas of Comparative Linguistics ['an open access database with lexical and typological/morphosyntactic data for historical, comparative and phylogenetic linguistics']
World Atlas of Language Structures (WALS) ['a large database of structural (phonological, grammatical, lexical) properties of languages gathered from descriptive materials (such as reference grammars) by a team of 55 authors']
MLA Language Map ['the locations and numbers of speakers of twelve languages commonly spoken in the United States']