It is very hard to give precise borders to the Chianti area in Tuscany. This is because the name of Chianti is traditionally refered to the area between Florence and Siena where Chianti wine has been produced and not a definite territorial area with boundaries. With time, the area where Chianti wine is produced has grown.
The map above is just to give you a rough idea of what is traditionally considered Chianti. The lines we've drawn are those of the borders of the comunes that traditionally are considered part of Chianti: Greve in Chianti, Radda in Chianti, Gaiole in Chianti, Castellina in Chianti, Castelnuovo Berardenga, Impruneta, San Casciano Val di Pesa, Tavernelle Val di Pesa, Barberino Val d'Elsa and Poggibonsi.
Parts of these areas, excluding Impruneta, grow the grapes that are transformed into "Chianti Classico DOCG" wine. If we go beyond the "Classico" area, Chianti wine has a total of 8 denominations, such as Colli Fiorentini, Colli Senesi and Chianti Rufina, to name just a few, that further extend the territory of Chianti as can be seen in this smaller map to the right.