Field note · March 24, 2025

sensor-telemetry.status: 3 values, 100.0% in the top three

3 values with 92.4% concentrated in one of them, and what that does to every chart downstream.

1 min read ·Visualization ·visualization practice

Distribution of status on sensor-telemetry, because every chart built on it inherits this shape.

  • ok — 7,394 rows, 92.4%
  • warn — 482 rows, 6.0%
  • fault — 124 rows, 1.6%

The top three take 100.0% between them. With only 3 values there is no tail to worry about, which makes this a genuinely easy column to chart.

sql
select status,
       count(*)                                      as rows,
       round(100.0 * count(*) / sum(count(*)) over (), 1) as pct,
       round(avg(temp_c)::numeric, 2)             as avg_temp_c
from sensor_telemetry
group by 1
order by rows desc;

The second column is the one that matters. Share of rows tells you what is common; avg_temp_c tells you whether the common thing is the important thing. They disagree more often than not, and a chart that shows only the first is answering the easier question.

Decide what happens to the tail before you plot it. "Other" as an explicit bucket is honest; twelve slivers is not, and neither is silently taking the top eight.