Practice

Choosing a chart

My notes on every way to show data: what each chart is good for, where it goes wrong, and how I pick between them. Built while studying Peter Walker’s 819 Carta charts for my data insights practice.

How I choose

1QuestionStart with something you’re curious about
2PickChoose the chart from the question
3Three versionsDifferent types, same data
4CompareWhich reads in three seconds?
5FrameSame header and footer every time
6Post and learnDo more of what lands

Then round again. Peter’s advice: make several versions, and scrap the first idea if the data says something else.

Start from the question

Tap any chart to see what it’s good for and where it goes wrong.

Comparing a few thingsHow big is it compared with that?

Labelled bars

Good for: 3 to 8 values, read exactly. The fastest chart to read.

Watch out: Two bars on their own is too thin to post. Start the axis at zero.

Mine: 10

Paired bars

Good for: Two measures per group, where the gap is the story.

Watch out: A third measure turns it into a mess.

Peter: who are venture LPs?

Dumbbell

Good for: Before and after for several groups at once.

Watch out: Say which dot is which. Separate scales need saying.

Mine: 02

Big-number tiles

Good for: Two to six headline stats on the same measure.

Watch out: No context on its own. Works when the tiles compare.

Peter: founder equity splits

Dot grid

Good for: Making a ratio feel real, like 17 to 1.

Watch out: Rounding. Say what one dot is worth.

Mine: exits, try 2

Showing the spreadWhat’s typical, and how wide is the range?

Range bars

Good for: Benchmarks by stage, city or sector: 25th, 50th, 75th.

Watch out: Most readers don’t know what a percentile is. Explain it once.

Peter: Series A valuations by city

Dot and whisker

Good for: The same, running left to right by stage.

Watch out: Crowded labels. Median big, ends small.

Peter: option pool by stage

Benchmark table

Good for: Numbers people will save and use in a negotiation.

Watch out: Dense on a phone. Box the median.

Peter: fundraising cheatsheet

Bubble table

Good for: Share of rounds in each size bucket, per stage.

Watch out: Circle sizes are hard to compare. Print the % inside.

Peter: valuation tiers

Histogram

Good for: "How rare is this?"

Watch out: The bucket sizes change the story. Pick them first.

Peter: $100M seeds are rare

Change over timeIs it going up, down, or apart?

Indexed lines

Good for: Two things in different units moving apart.

Watch out: The base year can exaggerate the gap. Show the base line.

Mine: 06

Stacked bars over time

Good for: A total and its parts, quarter by quarter.

Watch out: Only the bottom segment is easy to compare.

Mine: 01

Stacked area share

Good for: Two players splitting 100% over time.

Watch out: More than three layers and the middle gets lost.

Peter: Anthropic vs OpenAI

Lines with events

Good for: What happened when something launched.

Watch out: A marker suggests cause. Say if it’s only timing.

Peter: agentic share by week

Many lines, two lit

Good for: Context plus a story.

Watch out: Without greying the rest it’s spaghetti.

Peter: SAFEs won

Small multiples

Good for: The same chart for each stage, side by side.

Watch out: Tiny on phones. Share the axis.

Peter: valuations vs rounds

RankingWho’s on top, and who moved?

Ranked bars

Good for: Leaderboards that start an argument.

Watch out: Past about 15 rows it’s a wall. Box the row that matters.

Mine: 04, 10

Bump chart

Good for: Rank changing across stages or years.

Watch out: Hides the actual values. One line in colour.

Peter: Miami’s rise

Parts of a wholeWhat’s it made of?

100% stacked bars

Good for: Shares across several rows.

Watch out: Hides the totals. Put them in the subtitle.

Mine: 03

Stacks with brackets

Good for: Two groups of segments, like operators vs investors.

Watch out: More than five segments gets hard to read.

Peter: who owns a startup

RelationshipsHow do three things relate?

Bubble scatter

Good for: Three numbers at once, with median lines making quadrants.

Watch out: Bubbles overlap. Write the encoding on the chart.

Mine: 08

Labelled scatter

Good for: Named companies on two measures.

Watch out: Label every dot or it’s a guessing game.

Peter: founder ownership at IPO

CohortsWhere does a group end up?

Cohort funnel

Good for: "Class of 2018: where are they now?"

Watch out: Old cohorts tell you about old markets.

Mine: 09

Graduation heatmap

Good for: How fast each cohort reached the next round.

Watch out: Needs a how-to-read line and a deliberate colour scale.

Peter: Series A graduation

What I avoid

One number against oneTwo bars is a sentence. Put it in the post.

Pies with many slicesPeople can’t compare angles. Use a 100% bar.

Two y-axesYou can make any two lines cross. Index them instead.

Bars not starting at zeroSmall changes look huge.

Maps for rankingBig areas win attention, not big numbers.

A legend boxName the series in colour in the header.

Peter’s charts are Carta’s and OpenRouter’s, all public in Carta’s archive and on LinkedIn. The descriptions here are my notes. This page will change as I post more and learn what actually lands.