What it is
Chitta was historically the village record showing a survey number's land classification — nanjai (wet) or punjai (dry), among others such as natham or poramboke — along with its recorded extent, maintained separately from patta, which recorded ownership. Tamil Nadu has since merged the two into a single combined patta-chitta document, so the classification and ownership details that once sat in two separate registers now appear together on one record you request as a unit.
Why it matters when you buy
The classification recorded in the chitta portion tells you what the land is registered as — wet, dry, house-site, or government land — which affects what you can legally build or grow there and whether it needs reclassification before use. It's also where you cross-check the extent the seller has quoted against what the revenue department has on file; a gap between the two is worth resolving with the seller and, if needed, a surveyor before you pay anything.
Where you find it
Since the merger, chitta details are printed as part of the combined patta-chitta document available through eservices.tn.gov.in, Tamil Nadu's e-services portal. There is no separate standalone chitta certificate to request any more; asking for "patta chitta" against the survey number in question returns both the ownership and classification details together on the same document.
What it does not prove
The classification on a chitta records how the revenue department has the land registered, not what you are permitted to do with it. Land shown as nanjai or punjai has not thereby been cleared for building, and land shown as natham has not thereby been approved for a particular structure — that comes from the local planning authority, not from the revenue record. The extent shown is the recorded extent rather than a measured one, so where it differs from the sale deed or from what is fenced on the ground, the chitta does not settle which is right; an FMB sketch and a surveyor do.