Title: Pixel‑Perfect Parliament Diagrams in Adobe Illustrator — A Practical Guide for Graphic and Motion Designers
If you’ve ever tried to lay out hundreds of perfectly spaced dots in a clean semicircle, you know how fiddly it can be. Parliament (a.k.a. hemicycle) diagrams look simple, but getting the bottom edge to read as a smooth arc and keeping spacing consistent across rows is where most attempts fall apart.
This article is a designer‑friendly walkthrough of a new Illustrator script that builds flawless parliament diagrams in seconds. It’s tuned for production: crisp spacing, clean bottom edge, and adjustable geometry for print, broadcast, and motion graphics.
What you’ll get
- A ready‑to‑run Illustrator script that generates pro‑quality hemicycles.
- Controls for seat size, arc span, row density, margins, and centering.
- Reliable output you can color, label, export, and animate.
Background (in plain language)
We adapted the best ideas from three open‑source projects:
- slashme/parliamentdiagram — robust compositional thinking about how to manage rows, spacing, and blocks.
- elexnuk/arches — the cleanest “seat geometry” we’ve found; it keeps the bottom band visually perfect.
- Teester/parliament-diagram-generator — a thoughtful approach to distributing seats across rings.
Translated for designers, this means:
- The bottom edge is clean because each row trims its endpoints so dots don’t “flatten” into the baseline.
- Seats keep a consistent feel across rows (no bunching or drifting).
- The total seat count is respected while staying visually balanced.
What the script does
- Places dots along multiple concentric arcs (rows).
- Even spacing within each row (no overlaps).
- Optional “dense rows” mode to avoid skinny inner rows when your seat count is small.
- Works with any arc span (e.g., a 160°, 180°, or 200° hemicycle).
Installing the script
- macOS
- Save the file ParliamentDiagramGenerator.jsx.
- Move it to: Applications/Adobe Illustrator [version]/Presets/en_US/Scripts
- Restart Illustrator.
- Windows
- Save the file ParliamentDiagram_ArchesAdapted_v2.jsx.
- Move it to: C:\Program Files\Adobe\Adobe Illustrator [version]\Presets\en_US\Scripts
- Restart Illustrator.
- Alternative: File > Scripts > Other Script… (browse to the .jsx each time).
How to use
1) Open or create an Illustrator document.
2) Run: File > Scripts > Parliament (Arches‑adapted v2)
3) Set parameters:
- Total seats: the total number of dots you need.
- Seat diameter (pt): visual size of each dot. For broadcast 1080p, 6–12 pt is a good range.
- Span angle (deg): width of the arc (180 is a classic hemicycle; 160 feels a bit tighter).
- Force rows (0 = auto): leave at 0 to let the script pick; set a number if your art direction demands it.
- Dense rows: turns off unused inner rows so smaller totals look tight and intentional.
- Outer margin: padding from your diagram to the canvas edge.
- Centering: place the diagram dead‑center or aligned to your layout grid as needed.
Designer‑friendly recipes
- News lower‑third or small infographics
- 120–240 seats, 160° span, Dense rows ON
- Seat diameter 6–8 pt, Outer margin 24 pt
- Full‑screen broadcast explainer (1920×1080)
- 300–700 seats, 180° span, Dense rows OFF (to keep inner layers present)
- Seat diameter 8–12 pt
- A4/Letter print report
- 200–600 seats, 170–180° span
- Seat diameter 6–10 pt, Outer margin 18–24 pt
Coloring and labeling (fast workflows)
- Global color: Select the generated group and set Fill.
- Party color assignment:
- Quick way: Use the Lasso Tool to select contiguous seat clusters by row and recolor. Because spacing is uniform, selections are predictable.
- Methodical way: Ungroup once, then group rows (or arcs) and color by segments for consistent blocks.
- Labels: Add a centerline title or an outer arc legend. Keep text off the seat dots for clarity; place totals or party names just outside the curve.
Exporting for every medium
- Print/PDF: Save As > Adobe PDF (Preserve Illustrator Editing Capabilities ON if you’ll revise later).
- Web/SVG: Export As > SVG (Presentation Attributes ON, Responsive OFF for predictable sizes).
- Motion/After Effects:
- Import the .ai as Composition – Retain Layer Sizes.
- Convert to Shape Layers to animate stroke/fill or per‑row reveals.
- Add Trim Paths to build “row sweeps,” or use Opacity/Scale to pop in dots by arc.
Troubleshooting
- “Too tight at the bottom” or flattened edge
- Increase span angle a bit (e.g., 160 → 175).
- Increase Seat diameter slightly or toggle Dense rows ON.
- Overlapping dots on outer rows
- Reduce Seat diameter or increase Force rows by +1.
- Looks off‑center
- Turn off centering and place the group using your grid or guides.
- Performance with very large counts (1,000+)
- Reduce seat diameter, disable GPU preview temporarily, and keep the diagram in its own layer.
Why this looks better than most
- Constant‑chord spacing: Seats are positioned so the straight‑line distance between neighbors is consistent per row.
- End‑trim margins: Each row trims a small angle at both ends, preventing the bottom band from looking “crushed.”
- Capacity‑aware: The script calculates how many seats reasonably fit per row and distributes your total accordingly.
Accessibility and clarity tips
- Use color palettes with sufficient contrast for those with color‑vision deficiencies.
- Add a monochrome fallback or patterned overlays if the design must work in grayscale.
- Keep seat size consistent across related graphics so visual comparisons read correctly.
Roadmap ideas (tell us if you want these)
- Party data input (counts + colors) to auto‑color seats in order.
- “Staggered rows” style toggle for a different texture.
- Legend and total rendering as optional layers.
JavaScript
Download “ParliamentDiagramGenerator” ParliamentDiagramGenerator.zip – Downloaded 0 times – 3.00 KB
(function () {
if (app.documents.length === 0) {
alert("Open or create a document, then run the script again.");
return;
}
var doc = app.activeDocument;
// -------- UI --------
var dlg = new Window("dialog", "Parliament (Arches-adapted v2)");
dlg.orientation = "column";
dlg.alignChildren = "fill";
var p1 = dlg.add("panel", undefined, "Layout");
p1.orientation = "column"; p1.margins = 12;
var gSeats = p1.add("group");
gSeats.add("statictext", undefined, "Total seats:");
var uiSeats = gSeats.add("edittext", undefined, "577"); uiSeats.characters = 6;
var gSeatSize = p1.add("group");
gSeatSize.add("statictext", undefined, "Seat diameter (pt):");
var uiSeatDia = gSeatSize.add("edittext", undefined, "10"); uiSeatDia.characters = 6;
var gSpan = p1.add("group");
gSpan.add("statictext", undefined, "Span angle (deg):");
var uiSpan = gSpan.add("edittext", undefined, "180"); uiSpan.characters = 5;
var gForceRows = p1.add("group");
gForceRows.add("statictext", undefined, "Force rows (0=auto):");
var uiRows = gForceRows.add("edittext", undefined, "0"); uiRows.characters = 4;
var gDense = p1.add("group");
var uiDense = gDense.add("checkbox", undefined, "Dense rows (discard inner rows)");
uiDense.value = false;
var p2 = dlg.add("panel", undefined, "Canvas and options");
p2.orientation = "column"; p2.margins = 12;
var gMargin = p2.add("group");
gMargin.add("statictext", undefined, "Outer margin (pt):");
var uiMargin = gMargin.add("edittext", undefined, "24"); uiMargin.characters = 6;
var gCenter = p2.add("group");
var uiCenterHoriz = gCenter.add("checkbox", undefined, "Center horizontally");
uiCenterHoriz.value = true;
var uiCenterVert = gCenter.add("checkbox", undefined, "Center vertically");
uiCenterVert.value = true;
var gBtns = dlg.add("group");
gBtns.alignment = "right";
gBtns.add("button", undefined, "Cancel", { name: "cancel" });
var btnOk = gBtns.add("button", undefined, "Generate", { name: "ok" });
btnOk.onClick = function () {
var totalSeats = parseInt(uiSeats.text, 10);
var seatDiameterPt = parseFloat(uiSeatDia.text);
var spanAngleDeg = parseFloat(uiSpan.text);
var forceRows = parseInt(uiRows.text, 10);
var marginPt = parseFloat(uiMargin.text);
if (!(totalSeats > 0 && seatDiameterPt > 0 && marginPt >= 0) ||
isNaN(spanAngleDeg) || isNaN(forceRows)) {
alert("Please enter valid numeric values.");
return;
}
if (spanAngleDeg <= 0 || spanAngleDeg > 360) {
alert("Span angle must be in (0, 360].");
return;
}
dlg.close();
try {
generateDiagram({
totalSeats: totalSeats,
seatDiameterPt: seatDiameterPt,
spanAngleDeg: spanAngleDeg,
marginPt: marginPt,
forceRows: Math.max(0, forceRows),
denseRows: uiDense.value,
centerHoriz: uiCenterHoriz.value,
centerVert: uiCenterVert.value
});
} catch (e) {
alert("Error: " + e);
}
};
dlg.show();
// -------- Core geometry (arches generalized to any span) --------
function clamp(v, lo, hi) { return Math.max(lo, Math.min(hi, v)); }
function rowRadiusNormalized(R, i) {
// i = 1..R (1 is innermost)
return (3 * R + 4 * i - 2) / (4 * R);
}
function normalizedCircleRadius(R) { return 0.4 / R; }
function perRowCapacity(R, i, spanRad) {
var cR = normalizedCircleRadius(R);
var r = rowRadiusNormalized(R, i);
var ratio = clamp(cR / r, -1, 1);
var margin = Math.asin(ratio); // trim both ends
var avail = Math.max(0, spanRad - 2 * margin);
var step = 2 * Math.asin(ratio); // constant-chord spacing
if (step <= 0) return 1;
var n = Math.floor(avail / step) + 1;
return Math.max(1, n);
}
function totalCapacityForRows(R, spanRad) {
var sum = 0;
for (var i = 1; i <= R; i++) sum += perRowCapacity(R, i, spanRad);
return sum;
}
function chooseRowCount(totalSeats, spanRad) {
for (var R = 1; R <= 100; R++) {
if (totalCapacityForRows(R, spanRad) >= totalSeats) return R;
}
return 100;
}
// Dense rows optimization: discard inner rows to pack seats visually
function optimizeRows(totalSeats, R, spanRad) {
var handled = 0;
for (var i = R; i >= 1; i--) {
var cap = Math.floor(perRowCapacity(R, i, spanRad)); // integer capacity
handled += cap;
if (handled >= totalSeats) {
var wastedRows = i - 1; // rows 1..(i-1) discarded
var fullness = totalSeats / handled;
return { discard: wastedRows, fullness: fullness };
}
}
return { discard: 0, fullness: 0 };
}
function seatsPerRowDistribution(totalSeats, R, spanRad, dense) {
var caps = [];
for (var i = 1; i <= R; i++) caps.push(perRowCapacity(R, i, spanRad));
var startRow = 1;
var fullness;
if (dense) {
var opt = optimizeRows(totalSeats, R, spanRad);
startRow = opt.discard + 1;
fullness = opt.fullness;
} else {
var capSum = 0;
for (var j = 0; j < caps.length; j++) capSum += caps[j];
fullness = totalSeats / capSum;
}
var perRow = new Array(R);
for (var i = 0; i < R; i++) perRow[i] = 0;
var allocated = 0;
// Fill rows startRow..R-1 proportionally
for (var i = startRow; i <= R - 1; i++) {
var idx = i - 1;
var n = Math.floor(caps[idx] * fullness);
n = Math.min(n, caps[idx]);
perRow[idx] = n;
allocated += n;
}
// Last (outermost) row gets the remainder
perRow[R - 1] = Math.max(0, totalSeats - allocated);
return { perRow: perRow, startRow: startRow };
}
function appendSeatPositionsForRow(R, i, seatsInRow, spanRad, scale) {
// Returns array of [xPt, yPt]
var pts = [];
if (seatsInRow <= 0) return pts;
var cR = normalizedCircleRadius(R);
var rNorm = rowRadiusNormalized(R, i);
var ratio = clamp(cR / rNorm, -1, 1);
var margin = Math.asin(ratio);
var trimmedSpan = Math.max(0, spanRad - 2 * margin);
var rPt = rNorm * scale;
// Center the arc on π/2. The untrimmed arc endpoints are:
// L = (π - span)/2, H = (π + span)/2
// After trimming by margin on both sides:
var angleLow = (Math.PI - spanRad) / 2 + margin;
var angleHigh = (Math.PI + spanRad) / 2 - margin;
if (seatsInRow === 1 || trimmedSpan <= 0) {
var a = Math.PI / 2;
pts.push([rPt * Math.cos(a), rPt * Math.sin(a)]);
return pts;
}
var step = trimmedSpan / (seatsInRow - 1);
for (var j = 0; j < seatsInRow; j++) {
var angle = angleLow + j * step;
var x = rPt * Math.cos(angle);
var y = rPt * Math.sin(angle);
pts.push([x, y]);
}
return pts;
}
function buildAllSeatPositions(totalSeats, seatDiameterPt, spanAngleDeg, forceRows, denseRows) {
var spanRad = (spanAngleDeg * Math.PI) / 180;
var R = forceRows > 0 ? forceRows : chooseRowCount(totalSeats, spanRad);
var cR = normalizedCircleRadius(R);
var scale = seatDiameterPt / (2 * cR); // normalize -> pt
var dist = seatsPerRowDistribution(totalSeats, R, spanRad, denseRows);
var perRow = dist.perRow;
var startRow = dist.startRow;
var pts = [];
for (var i = startRow; i <= R; i++) {
var nRow = perRow[i - 1] || 0;
if (nRow <= 0) continue;
var rowPts = appendSeatPositionsForRow(R, i, nRow, spanRad, scale);
pts = pts.concat(rowPts);
}
return { positions: pts, scale: scale };
}
// -------- Rendering --------
function generateDiagram(opts) {
var totalSeats = opts.totalSeats;
var seatDia = opts.seatDiameterPt;
var spanAngleDeg = opts.spanAngleDeg;
var marginPt = opts.marginPt;
var built = buildAllSeatPositions(
totalSeats,
seatDia,
spanAngleDeg,
opts.forceRows,
opts.denseRows
);
var pts = built.positions;
var layer = doc.activeLayer;
var group = layer.groupItems.add();
group.name = "Parliament (" + totalSeats + ", " + spanAngleDeg + "°)";
var fillColor = new RGBColor(); fillColor.red = 0; fillColor.green = 0; fillColor.blue = 0;
var r = seatDia / 2;
// Bounds for centering
var minX = 1e9, maxX = -1e9, minY = 1e9, maxY = -1e9;
for (var i = 0; i < pts.length; i++) {
var cx = pts[i][0], cy = pts[i][1];
if (cx < minX) minX = cx; if (cx > maxX) maxX = cx;
if (cy < minY) minY = cy; if (cy > maxY) maxY = cy;
var seat = group.pathItems.ellipse(cy + r, cx - r, seatDia, seatDia);
seat.stroked = false;
seat.filled = true;
seat.fillColor = fillColor;
}
// Centering
var gx = (minX + maxX) / 2;
var gy = (minY + maxY) / 2;
var targetX = opts.centerHoriz ? (doc.width / 2) : (opts.marginPt + (maxX - minX) / 2);
var diagramHeight = (maxY - minY) + 2 * r;
var targetY = opts.centerVert ? (doc.height / 2) : (opts.marginPt + diagramHeight / 2);
group.translate(targetX - gx, targetY - gy);
app.redraw();
}
})();
