Dilip:
Having banged my head against the same brick wall, I agree broadly
with what you have said. I have a few additional points, though.
1. If one wants a single village or few villages to be mapped, one
can try to use the village cadastral maps. It is laborious, because
again the maps are not georeferenced, but feasible with some ground
data. Even here, errors are significant: 100s of meters often
(especially for common lands/forest lands on the edges of villages,
and especially in hilly areas)
2. The only publicly available source of village boundary maps (a
full sheet of polygons) is the district census handbook, which
contain 1 page each showing all the villages in a taluka (or
sometimes CD block). They in turn have only sourced this from the
directorate of land records and survey settlement in each state. We
spoke to the directorate in karnataka, and the way they have created
these taluka-level maps was to lay down all the individual village
cadastral maps on the floor and piece them together like a jigsaw
puzzle. of course they could not do this very precisely--they were
left with gaps and overlaps, and they simply 'adjusted' them as best
as possible. These 'puzzles' covered the whole floor of a big hall
(because a taluka may contain 100 villages) and then they 'reduced'
the hall size map to a page using analog drawing techniques. So the
census/DLS maps are quite crude. As Dilip says: adequate to let you
know which village is where, and what is its approximate shape, but
area of the polygon can differ from cadastral map areas by upto 50%.
To add to the problem: census has been very inconsistent in the way
they deal with uninhabited villages: sometimes showing them,
sometimes not, etc.
3. I don't quite agree with Dilip about habitation: It is true that
folks owning land in village A may actually live in village B. As an
extreme version of this, it can happen that village A may have zero
population, but non-zero cultivated land, because all the
cultivators live in village B. But the 'settlement' of a village by
definition has to lie within its boundary, because settlement refers
by definition to the people living in the village (not all people
owning land in the village).
4. So also I don't understand Dilip's point 5 about habitations
merging. Sure: settlement be side by side and physically contiguous
across a revenue village boundary, but that to me is not an issue:
census, if properly done, will put the two sets of households in
their respective villages.
5. Frankly, at this point, I would be happy even if NRSC/Bhuvan and
others released a polygon layer of 2011 and 2001 village polygons
AS IT IS, but with consistent and complete numbering of polygons,
and georeferenced to the best of their ability (with a statement
about how much error is expected).
6. HOWEVER, THERE IS MORE ACCURATE DATA, IT IS JUST NOT BEING PUT IN
THE PUBLIC DOMAIN:
a) most states have land record digitisation which now includes
digitization of cadastral maps. But they either don't share it at
all, or charge you huge amounts for it, even though it is created
with public money. of course, cadastral data are i) not
georeferenced, and ii) out of date, iii) one village at a time
(which when combined with the non-georeferenced nature make things
difficult to put together. But again, something would be better than
nothing.
b) NRSC and/or state agencies are working on projects to
georeference village boundaries and individual parcels. No one knows
how far they have gone in each state, how good their work is, and
cerrtainly none of it is in the public domain. But it is there, and
we must constantly push to get access to it as a matter of right.
c) Many individual programmes/projects such as watershed
development, irrigation, agriculture department projects do their
own digitisation and georeferencing. Again, they refuse to share it.
d) Census 2011 had put out a ppt claiming (for towns) they have even
mapped individual streets and buildings (I had posted the link to
this ppt some years ago), but when we asked them, they denied any
knowledge about it!
7) About whether accurate data is every possible: the problem is not
technical or even one of quality control in implementation. The
problem is inherently political: folks in villages or towns have
always opposed rigorous surveying because they think they stand to
lose, or might get punished when their encroachments come to light,
etc. DLR-Karnataka ran a pilot project which took them 6 months per
village because of this kind of opposition.
Sharad