R Graphics · Polygon Plot

Drawing Filled Shapes and Areas with Polygons in R

Learn closed shapes, transparent overlays, areas under curves, confidence bands, highlighted regions, and layered polygons.

6 examplesReproducible R code

Before you begin

Choose the variation that serves the analysis

polygon() joins ordered coordinates into a closed shape. It is a versatile low-level tool for filled regions, uncertainty bands, map-like shapes, and emphasis within an existing plot.

Examples: 06
Levels: Beginner + Intermediate

Example 01Base RBeginner

Draw a Basic Polygon

A polygon connects coordinate pairs and closes the final edge automatically.

Provide x and y vectors in boundary order. Fill and border colors define the interior and outline.

RRun this code

plot(1, type = "n", xlim = c(0, 5), ylim = c(0, 5), xlab = "X", ylab = "Y")
polygon(c(1, 4, 3.5, 2, .7), c(1, 1.2, 4, 4.5, 3),
        col = "#60a5fa", border = "#172554", lwd = 2)

Example 02Base RBeginner

Overlay Transparent Polygons

Transparency allows overlapping regions to remain visible.

adjustcolor() adds alpha transparency, making intersections legible without requiring a separate pattern.

RRun this code

plot(1, type = "n", xlim = c(0, 7), ylim = c(0, 5), axes = FALSE, xlab = "", ylab = "")
polygon(c(1,4,3,1), c(1,1,4,1), col = adjustcolor("#2563eb",.45), border = "#2563eb")
polygon(c(3,6,5,3), c(1,1,4,1), col = adjustcolor("#f59e0b",.45), border = "#f59e0b")

Example 03Base RBeginner

Shade the Area Under a Curve

A filled polygon can emphasize accumulated area beneath a line.

Combine the curve coordinates with baseline endpoints so the polygon closes along the axis.

RRun this code

x <- seq(0, 2*pi, length.out = 150); y <- sin(x) + 1
plot(x, y, type = "n", xlab = "x", ylab = "sin(x) + 1")
polygon(c(x, rev(x)), c(y, rep(0, length(y))), col = "#dbeafe", border = NA)
lines(x, y, col = "#2563eb", lwd = 3)

Example 04Base RIntermediate

Construct a Confidence Band

Two boundaries can be joined into one polygon representing uncertainty.

Append the upper boundary to the reversed lower boundary so the shape does not cross itself.

RRun this code

x <- 1:30; fit <- 2 + .2*x; se <- .5 + x/100
plot(x, fit, type = "n", ylim = range(fit-se, fit+se))
polygon(c(x, rev(x)), c(fit-se, rev(fit+se)), col = adjustcolor("#2563eb",.2), border = NA)
lines(x, fit, col = "#2563eb", lwd = 3)

Example 05Base RIntermediate

Highlight a Region of Interest

A rectangle-shaped polygon can mark a meaningful interval behind the data.

Draw the highlighted region before the series and use transparency so gridlines and values remain readable.

RRun this code

x <- 1:20; y <- cumsum(rnorm(20))
plot(x, y, type = "n")
polygon(c(8, 13, 13, 8), c(par("usr")[3], par("usr")[3], par("usr")[4], par("usr")[4]),
        col = adjustcolor("#f59e0b",.2), border = NA)
lines(x, y, col = "#172554", lwd = 2)

Example 06Base RIntermediate

Build a Layered Polygon Composition

Multiple polygons can form a richer analytical or illustrative graphic.

Control the drawing order: background shapes first, then foreground shapes, outlines, and annotations.

RRun this code

plot(1, type = "n", xlim = c(0, 10), ylim = c(0, 6), axes = FALSE, xlab = "", ylab = "")
polygon(c(0,3,5,7,10,10,0), c(1,4,2.5,5,2,0,0), col = "#dbeafe", border = NA)
polygon(c(0,3,5,7,10,10,0), c(.5,2.5,1.5,3,1,0,0), col = "#2563eb", border = NA)