Geographic line (isogloss) between dialects in northern France
The Joret line (French: ligne Joret; Norman: lène Joret:Picard: line Joret) is an isogloss that divides the langues d'oïl. Dialects north and west of it preserve Latin /k/ and /ɡ/ before /a/; dialects south and east of it palatalize them. In Old French the result of this palatalisation was /t͡ʃ/ and /d͡ʒ/ (for original /k/ and /ɡ/ respectively), which yield /ʃ/ and /ʒ/ in Modern French. The line was first identified by Charles Joret and published in 1883.
The area north and west of it is sometimes called the 'Normano-Picard domain' (French: domaine normano-picard). Within it lie Picard and the northern dialects of Norman.
Norman Picard /k/ ~ Southern Norman, French /ʃ/, Walloon /tʃ/ (palatalization)
Latin cattu (cat) gave rise to /ka/cat north of the line and /ʃa/chat to the south.
Low Latin *captiare (to catch) gave rise to cachier / cacher (> English catch) north of the line and chasser (> English chase) to the south.
Low Latin *cantionem (song), Picard canchon West of the line, French chanson, Walloon tchinson South and East of the line. Similarly Latin cantare → canter vs. chanter, tchanter.
Frankish *pokka (bag) gave rise to /puk/pouque (> English dial. poke) north of the line and pouche (> English pouch) to the south. French poche (pocket), Norman pouquette (> English pocket).
Latin candela (candle) gave rise to candelle north of the line and chandelle to the south.
Celtic *carros > Latin carrus gave rise to car (> English car) north of the line and char (wain, carriage), chariot (> English chariot) to the south.
Celtic *kagio-, Gaulish caio- > Norman Picard kay, cay (> ME kay) > French quai (> English quay); Old French chay > French chai (wine cellar)
Norman Picard /ɡ/ ~ Southern Norman, French /ʒ/, Walloon /dʒ/ (palatalization)
Latin gamba (leg) gave rise to /ɡãb/gambe north of the line and /ʒãb/jambe to the south, djambe to the East.
Frankish *gard- (yard) gave rise to gardin (> English garden) north of the line and jardin to the south.
Late Latin *galleto > Norman Picard gal(l)on (> English gallon) ; Old French jallon , French jalon (measure)
Second isogloss
Another effect of the palatalizations a bit further to the north but quite parallel was this:
Norman Picard /ʃ/ (or /tʃ/) ~ Southern Norman /ts/ or /s/, French /s/.
Low Latin *captiare > Norman Picard cacher, cachi(er) (> English catch); Southern Norman, French chasser
Low Latin ceresiu(m) > Norman Picard cherise, chrise, chise (> English cherry); Southern Norman srise French cerise
Third isogloss
A third isogloss, marking a consonantal change unrelated to the others, more or less follows the Joret line throughout Normandy and continues through northeastern France. It includes all of Picardy, Wallonia, Champagne, Lorraine and a part of Burgundy.
Germanic /w/ (sometimes Latin /v/ was affected as well) was kept north of the line (written w or v), but became /ɡ/ (written g or gu) south of the line.
Northern French /v/ ~ French /ɡ/
Latin vespa / Frankish *waspa (wasp) > Picard Wespe, Norman Vêpe ~ French guêpe (wasp)
Frankish *wala hlaupan (S. English well and leap) > Picard, Old Norman waloper (> English wallop) ; French galoper (> English gallop)
Frankish wahtôn (S. English wake and watch) > Picard Old Norman wait(i)er (> English wait) ; Old French guaitier, French guetter
Frankish *werra > Old Picard Old Norman werre, warre (> English war) ; French guerre (war)
Norman placenames derived from the Gallo-Romance word Campaniacum show initial C- in some cases (Campigny, north) and initial Ch- in others (Champigny-la-Futelaye, south).