A calendar heatmap visualizes time-series data on a calendar grid, where each day is represented as a cell and color intensity indicates the value magnitude. The layout follows a calendar structure with days as cells, weeks as rows, and months as columns or sections. This visualization excels at revealing daily patterns, seasonal trends, and temporal anomalies over extended time periods.
# anyplot.ai
# heatmap-calendar: Basic Calendar Heatmap
# Library: makie 0.21.9 | Julia 1.11.9
# Quality: 89/100 | Created: 2026-07-24
using CairoMakie
using Colors
using Dates
using Random
Random.seed!(42)
# --- Theme tokens -----------------------------------------------------------
const THEME = get(ENV, "ANYPLOT_THEME", "light")
const PAGE_BG = THEME == "light" ? colorant"#FAF8F1" : colorant"#1A1A17"
const INK = THEME == "light" ? colorant"#1A1A17" : colorant"#F0EFE8"
const INK_SOFT = THEME == "light" ? colorant"#4A4A44" : colorant"#B8B7B0"
# Imprint sequential colormap (single-polarity) — brand green → blue.
# Daily commit counts are single-polarity magnitude, so imprint_seq applies.
const IMPRINT_SEQ = cgrad([colorant"#009E73", colorant"#4467A3"])
# Faint neutral for calendar cells outside the data range (missing days).
const EMPTY_CELL = RGBAf(INK.r, INK.g, INK.b, 0.06)
# --- Data -------------------------------------------------------------------
# GitHub-style contribution graph: one year of daily commit counts.
start_date = Date(2025, 1, 1)
end_date = Date(2025, 12, 31)
all_dates = start_date:Day(1):end_date
commits_by_date = Dict{Date,Int}()
for d in all_dates
weekday_base = dayofweek(d) <= 5 ? 6.0 : 0.5 # weekdays busy, weekends quiet
yearly_trend = 10.0 * (dayofyear(d) / 365) # activity grows over the year
seasonal = 5.0 * sin(2π * (dayofyear(d) - 80) / 365) # spring/autumn peaks
count = round(Int, max(0.0, weekday_base + yearly_trend + seasonal + randn() * 2.5))
rand() < 0.08 && (count = 0) # occasional rest day
commits_by_date[d] = count
end
vmax = maximum(values(commits_by_date))
# Calendar grid geometry: columns = weeks, rows = weekdays (Mon..Sun).
first_monday = start_date - Day(dayofweek(start_date) - 1)
n_weeks = div((end_date - first_monday).value, 7) + 1
cell_rects = Rect2f[]
cell_colors = RGBAf[]
pad = 0.09
for week in 0:(n_weeks - 1), row in 1:7
day = first_monday + Day(week * 7 + (row - 1))
push!(cell_rects, Rect2f(week - 0.5 + pad, row - 0.5 + pad, 1 - 2pad, 1 - 2pad))
if start_date <= day <= end_date
push!(cell_colors, RGBAf(get(IMPRINT_SEQ, commits_by_date[day] / vmax)))
else
push!(cell_colors, EMPTY_CELL)
end
end
# Month labels centered over each month's mid-point week (shown along the top).
month_positions = Float64[]
month_labels = String[]
for m in 1:12
mid = Date(2025, m, 15)
push!(month_positions, div((mid - first_monday).value, 7))
push!(month_labels, monthabbr(mid))
end
# --- Plot -------------------------------------------------------------------
fig = Figure(
size = (1600, 900),
fontsize = 16,
backgroundcolor = PAGE_BG,
figure_padding = (44, 44, 30, 30),
)
# Flexible spacer rows above (row 1) and below (row 4) the fixed calendar (row 2)
# and legend (row 3) center the whole block, filling the 16:9 canvas evenly.
Box(fig[1, 1]; color = :transparent, strokewidth = 0, tellheight = false)
ax = Axis(
fig[2, 1];
title = "heatmap-calendar · julia · makie · anyplot.ai",
titlesize = 26,
titlecolor = INK,
titlegap = 16,
backgroundcolor = PAGE_BG,
yreversed = true, # Monday at the top row
xaxisposition = :top,
xticks = (month_positions, month_labels),
yticks = (1:7, ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]),
xticklabelsize = 19,
yticklabelsize = 19,
xticklabelcolor = INK_SOFT,
yticklabelcolor = INK_SOFT,
xticksvisible = false,
yticksvisible = false,
xgridvisible = false,
ygridvisible = false,
)
hidespines!(ax)
poly!(ax, cell_rects; color = cell_colors, strokewidth = 0)
xlims!(ax, -0.7, n_weeks - 0.3)
ylims!(ax, 7.7, 0.3)
# Sequential legend for value interpretation.
Colorbar(
fig[3, 1];
colormap = IMPRINT_SEQ,
limits = (0, vmax),
vertical = false,
flipaxis = false,
label = "Daily commits",
labelcolor = INK,
labelsize = 18,
ticklabelcolor = INK_SOFT,
ticklabelsize = 15,
tickcolor = INK_SOFT,
width = Relative(0.4),
height = 18,
)
Box(fig[4, 1]; color = :transparent, strokewidth = 0, tellheight = false)
# Fixed content-row heights (stretched, taller-than-wide cells) keep the calendar
# and legend adjacent; the flexible spacers absorb the rest, so no empty mid-band.
rowsize!(fig.layout, 2, Fixed(560))
rowsize!(fig.layout, 3, Fixed(40))
rowgap!(fig.layout, 16)
# --- Save -------------------------------------------------------------------
save("plot-$(THEME).png", fig; px_per_unit = 2)
Runnable source as JSON, for any HTTP client: https://api.anyplot.ai/specs/heatmap-calendar/makie/code. Any spec id and library id listed in llms-full.txt fit the same URL shape; every URL below is complete and callable.
{
"spec_id": "heatmap-calendar",
"language": "julia",
"library": "makie",
"page": "https://anyplot.ai/heatmap-calendar/julia/makie",
"hub": "https://anyplot.ai/heatmap-calendar",
"code_json": "https://api.anyplot.ai/specs/heatmap-calendar/makie/code",
"spec_json": "https://api.anyplot.ai/specs/heatmap-calendar",
"render_light_png": "https://storage.googleapis.com/anyplot-images/plots/heatmap-calendar/julia/makie/plot-light.png",
"render_dark_png": "https://storage.googleapis.com/anyplot-images/plots/heatmap-calendar/julia/makie/plot-dark.png",
"quality_score": 89.0,
"license": "MIT",
"guide": "https://anyplot.ai/llms.txt"
}Part of Basic Calendar Heatmap on anyplot.ai.