What this archive cannot tell you

The territory shares

Every seat record lists the constituencies its territory went to, or came from, with a percentage attached. Those percentages are computed by intersecting the mapped boundaries of the two delimitation orders, which are drawn on a single projection for each state. They are measurements of the maps, not readings from the delimitation order.

Three things follow, and all three matter if you intend to use the numbers.

The shares are areal. They describe land, not people. A successor seat drawing forty per cent of its area from a predecessor may draw a far larger or far smaller proportion of its electors, because density varies enormously between a city ward and a rural tract. Anyone back-casting election results across the two orders needs to weight by population, and this archive does not supply that weighting.

The two directions are different numbers. On a pre-delimitation seat the figure is the share of that seat which went to each successor. On a post-delimitation seat it is the share of that seat drawn from each predecessor. A seat can send ninety per cent of itself somewhere and still account for only ten per cent of the destination.

The figures do not sum to one hundred. Overlaps below one per cent are dropped as slivers, and the record shows only the lineage links that have been curated. The maps commonly show further partial overlaps that no source describes as a successor relationship.

Why some shares carry a tilde

A figure shown as ~22% is approximate. It means at least one of the two seats is defined by municipal wards, and the two orders number wards on incompatible schemes. The boundary cannot be matched mechanically, so the figure indicates scale rather than a measurement you should quote.

A small number of links carry no percentage at all. That is deliberate. Where the computed overlap fell below half a per cent on a link the delimitation order supports, printing a figure would imply a precision the geometry does not have. The link is shown; the number is withheld.

The maps

Pre-delimitation boundaries are digitised from a pre-2008 all-India assembly-constituency shapefile. Post-delimitation boundaries come from the Election Commission's published polygons. The two were drawn for different purposes at different times, and they do not register perfectly against one another.

Three constituencies have a record on this site but no polygon, and so appear in no share calculation at all: Maharashtra AC 148 Amgaon and AC 278 Ichalkaranji, and Karnataka AC 203 Sankeshwar.

Maharashtra's two layers show materially more displacement between them than any other state's. Its shares should be read with more caution than the rest.

Bangalore's pre-delimitation boundaries are wrong, and knowingly so. The city's two layers agree in aggregate, but the individual pre-2008 city seats are misplaced within it. Tested against the 2008 order, the mapped area of the old Chamarajapet, Malleswaram and Jayamahal constituencies falls almost entirely inside the new Yelahanka constituency, which lies well to the north of all three. That cannot be a genuine redraw; it is a fault in the digitised source.

No territory share is therefore published for any constituency in Bangalore district, under either order. The lineage links between old and new Bangalore seats are still shown, because those are curated from the order text rather than measured from the maps, but they carry no percentage. Plate I should not be read as an accurate depiction of where Bangalore's pre-2008 constituencies lay.

The status field

Each pre-delimitation seat is marked continuing, renamed or abolished, and each post-delimitation seat continuing, renamed or new. The field tracks the name, not the territory. A seat whose name survived is marked continuing even where the redraw left little of its original ground, which is common for city seats reduced to their municipal core.

A seat that split into halves carrying a qualifier, such as a city and a rural counterpart, is treated as abolished rather than renamed: it did not change its name, it ceased to exist. Only a genuine change to the name itself counts as a rename. This convention is applied uniformly across every state.

Sources

Constituency composition is taken from the Delimitation of Parliamentary and Assembly Constituencies Orders of 1976 and 2008. Winners and electorate figures are from the Election Commission's statistical reports for the relevant state elections. Boundaries are as described above. Each state page lists its own sources and caveats in full.