On Constituency Charts time is displayed as proceeding from left to right. Years are only shown on a given Constituency Chart for those General Elections when there were changes to the constituencies on the chart big enough to be shown as a transfer line (see below). For example, although there were widespread changes to constituency boundaries in 1955, these are not shown in Chart 1 (Brent, Westminster and City of London), as the constituencies in that group remained unchanged in 1955.
Transfers to or from other groups of constituencies are shown as being to or from an area with a white background, with the constituency name in another group being shown in italics with the group number, and with a dashed border.
Multi-member constituencies are shown with an appropriate size reflecting the number of MPs elected for the constituency. For example, the City of London between 1885 and 1950 in Chart 1 is shown twice the size of the other constituencies, as it was a two member constituency for this period.
The size of transfer is shown based on the estimated relative percentage of the electorate in a constituency that has come from each of its predecessors. The following conventions are used to denote the size of the transfer on the Constituency Chart:
<3% of the electorate of new constituency: no line is shown;
3% - 10%: a thin dashed black line;
10% - 30%: a thin solid black line;
30% - 65%: a thicker solid black line;
>65%: a thick red line. (A constituency joined by a thick red line to an earlier one is considered its natural successor, and where possible is kept at the same level on the Constituency Chart. For this reason, at most one thick red line is shown as coming from any constituency. If there are two or more constituencies such that more than 65% of each is from the same predecessor seat, a thick red line will be shown emanating from the predecessor only if more than 65% of the predecessor went to a particular constituency.)
Irrespective of the above, each constituency at a given time must have at least one solid line linking it to another constituency.
The transfer of a complete Borough (or Burgh in Scotland) is also always shown as a line, even if below the 3% threshold.
For example, in Chart 1 (Brent, Westminster and City of London), no line is shown for sub-Areas areas 43 and 44 (on the Area Map) which transferred to Cities of London & Westminster from, respectively, Islington S & Finsbury and Bethnal Green & Stepney in 1997, as both of these transfers are below the 3% threshold.