In this guide
A chart turns a table into a story quickly. That speed is useful, but it can hide choices about scale, categories and missing information. Municipal employees who prepare briefings should inspect those choices before interpreting a line or ranking a bar. This is an editorial review method, not a claim that any particular Phoenix chart is misleading.
Read the labels as part of the evidence
Identify the unit, period and population. A line labeled “requests” may count submissions, unique cases or completed actions. If the label is too short to tell, look for the accompanying definition. The chart's title alone should not carry the entire explanation.
Phoenix's public data-and-evidence resources show the institutional context for performance information. A reader still needs the metadata of the individual display. A reputable publisher does not make every chart suitable for every question; the fit between measure and question remains the analyst's responsibility.
Inspect scale before describing magnitude
An axis that begins above zero can emphasize a small difference. That may be appropriate for a particular line chart, but the reader should understand it. A bar chart with truncated values can be especially easy to misread as a proportional comparison. Describe the actual values rather than relying only on the visual impression.
For a hypothetical exercise, draw values of 98 and 100 on two different vertical scales. The difference is always two units even when the pictures feel very different. Ask a peer to state the numerical change before discussing what the image suggests. The exercise teaches attention to display, not a universal ban on a particular axis choice.
Distinguish zero from missing
A blank cell may mean unavailable, not applicable, suppressed or not yet reported. Replacing it with zero invents information. Joining a line across a gap can also imply continuity that the source did not establish. Preserve the source's missing-value convention and explain it in the caption.
If the convention is unclear, leave the gap and ask the data owner. Do not reverse-engineer a value from the shape you expect. Municipal readers need to know whether a chart reflects observed activity or the present limits of reporting.
Write a caption that survives forwarding
A useful caption includes the measure, period, unit, source and important caveat. It should remain attached when the image is pasted into a slide. Avoid captions that merely repeat the title while the essential qualification remains in a separate document.
Before sharing, test whether a colleague can explain what the chart shows and what it cannot establish. If they infer a staffing judgment, causal story or service promise that the evidence does not support, revise the caption or the display. Clear visualization narrows misunderstanding instead of decorating it.
Sources and limits
Official public sources checked October 5, 2026. Examples and exercises are original editorial illustrations, not City records or instructions.
- Improving Phoenix with Data and Evidence
Published data and performance initiatives. Exercise datasets are explicitly hypothetical, not Phoenix performance claims.