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Posted to notifications@superset.apache.org by "alex-poor (via GitHub)" <gi...@apache.org> on 2026/06/05 03:44:50 UTC
[I] Deck.gl Polygon legend labels share endpoints (cosmetic / ambiguous range labels) [superset]
alex-poor opened a new issue, #40786:
URL: https://github.com/apache/superset/issues/40786
### Bug description
The deck.gl **Polygon** chart legend renders bucket labels with **shared endpoints**, so consecutive bins appear to overlap. With default settings (no manual break points), the legend shows e.g.:
```
1 - 81
81 - 212
212 - 369
```
Every interior breakpoint (`81`, `212`, …) appears in **two** adjacent labels — once as an upper bound, once as a lower bound — which reads as overlapping ranges and is confusing.
**This is a cosmetic / UX-clarity issue, not a correctness bug.** The underlying binning and coloring are correct: colors are assigned with d3's `scaleThreshold`, which treats each breakpoint as a half-open cut point, so a value of exactly `81` lands in exactly one bucket (`81–212`). No polygon is double-counted or mis-colored. Only the legend *label text* is ambiguous.
### Root cause
In `superset-frontend/plugins/preset-chart-deckgl/src/utils.ts`, `getBuckets()` builds each label by pairing adjacent breakpoints:
```js
const range = `${breakPoints[i]} - ${breakPoints[i + 1]}`;
```
This always reuses each interior breakpoint in two labels. The color scale (`getBreakPointColorScaler`, same file) uses `scaleThreshold`, which is half-open and unambiguous — so the labels misrepresent the (correct) bucketing logic.
### Scope
- Affects the deck.gl **Polygon** layer only — it is the only chart in the frontend that renders a **discrete numeric-range legend** (`scaleThreshold` appears nowhere else in `superset-frontend`).
- Country Map / World Map avoid this by using a **continuous linear color scale** with no discrete-range legend.
- ECharts charts use **categorical** legends (names, not ranges), so they are unaffected.
- Independent of the `Number of buckets` vs `Bucket break points` controls — setting explicit break points changes *where* the bins are, but labels still share endpoints.
### Expected behavior
Legend bins should read as a clean, non-overlapping partition. There is no existing internal convention to match (Polygon is the only discrete-range legend), so candidate formats:
1. **Edge-operator notation** (common GIS/choropleth convention — ArcGIS, Datawrapper): `< 81`, `81 – 212`, `212 – 369`, `> 369`
2. **Interval notation:** `[1, 81)`, `[81, 212)`, `[212, 369]`
3. **Render the boundary number once between touching swatches** (gradient-bar style) rather than as isolated `a - b` rows.
> Note: simply incrementing the lower bound (`82 - 212`) is *not* correct in general — breakpoints and metric values can be fractional, so a value like `81.5` would fall into a labeling gap.
### How to reproduce
1. Create a deck.gl **Polygon** chart with a numeric metric.
2. Leave **Bucket break points** empty (use default **Number of buckets**).
3. Observe the legend — adjacent bins share endpoints (`1 - 81`, `81 - 212`, …).
### Superset version
master / latest (also observed on 5.0+).
### Related (different) issues
- #34747 — legend *limits* miscalculated (rounding the max bound); a separate, already-fixed bug.
- #7264, #35142 — other deck.gl legend fixes; none address label formatting.
No existing open issue/PR covers the shared-endpoint label formatting.
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Re: [I] Deck.gl Polygon legend labels share endpoints (cosmetic / ambiguous range labels) [superset]
Posted by "rusackas (via GitHub)" <gi...@apache.org>.
rusackas closed issue #40786: Deck.gl Polygon legend labels share endpoints (cosmetic / ambiguous range labels)
URL: https://github.com/apache/superset/issues/40786
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Re: [I] Deck.gl Polygon legend labels share endpoints (cosmetic / ambiguous range labels) [superset]
Posted by "rabumaabraham (via GitHub)" <gi...@apache.org>.
rabumaabraham commented on issue #40786:
URL: https://github.com/apache/superset/issues/40786#issuecomment-4644094434
Hi, I'm working on this issue and will submit a PR soon. Please assign it to me if possible, thanks!
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Re: [I] Deck.gl Polygon legend labels share endpoints (cosmetic / ambiguous range labels) [superset]
Posted by "sadpandajoe (via GitHub)" <gi...@apache.org>.
sadpandajoe commented on issue #40786:
URL: https://github.com/apache/superset/issues/40786#issuecomment-4633816920
@dosubot help debug this
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Re: [I] Deck.gl Polygon legend labels share endpoints (cosmetic / ambiguous range labels) [superset]
Posted by "dosubot[bot] (via GitHub)" <gi...@apache.org>.
dosubot[bot] commented on issue #40786:
URL: https://github.com/apache/superset/issues/40786#issuecomment-4633836575
<!-- Answer -->
Here's the full debug breakdown of the shared-endpoint label issue:
**The problematic code** is in `getBuckets()` at `superset-frontend/plugins/preset-chart-deckgl/src/utils.ts` [[1]](https://github.com/apache/superset/blob/829e4d92d91ceae4b43b1ed3b063ffe45377799c/superset-frontend/plugins/legacy-preset-chart-deckgl/src/utils.ts#L179-L180):
```typescript
breakPoints.slice(1).forEach((_, i) => {
const range = `${breakPoints[i]} - ${breakPoints[i + 1]}`;
...
});
```
This pairs adjacent breakpoints directly, so for breakpoints `[1, 81, 212, 369]` you get `"1 - 81"`, `"81 - 212"`, `"212 - 369"` — each interior value appears in two labels.
**The color scale** uses D3's `scaleThreshold` [[2]](https://github.com/apache/superset/blob/829e4d92d91ceae4b43b1ed3b063ffe45377799c/superset-frontend/plugins/legacy-preset-chart-deckgl/src/utils.ts#L87-L166), which creates left-inclusive / right-exclusive intervals:
- `[1, 81)` → color 0
- `[81, 212)` → color 1
- `[212, 369]` → color 2
So a value of exactly `81` lands in bucket 2, not bucket 1. The bucketing is correct; only the labels are ambiguous.
**Breakpoint generation** (`getBreakPoints`, [[3]](https://github.com/apache/superset/blob/829e4d92d91ceae4b43b1ed3b063ffe45377799c/superset-frontend/plugins/legacy-preset-chart-deckgl/src/utils.ts#L42-L85)) computes evenly spaced values using `(startValue + i * delta).toFixed(precision)`, where precision is derived from `Math.ceil(Math.log10(1 / delta))`. These can be fractional strings, which is why a naive "lower + 1" fix doesn't generalize.
**Legend rendering** — the `formatCategoryLabel` function [[4]](https://github.com/apache/superset/blob/829e4d92d91ceae4b43b1ed3b063ffe45377799c/superset-frontend/plugins/legacy-preset-chart-deckgl/src/components/Legend.tsx#L85-L97) splits each range on `" - "` and formats each number, then the Legend component renders them as color-swatch rows [[5]](https://github.com/apache/superset/blob/829e4d92d91ceae4b43b1ed3b063ffe45377799c/superset-frontend/plugins/legacy-preset-chart-deckgl/src/components/Legend.tsx#L103-L119).
**A minimal fix** would be localized to `getBuckets()`. For example, using the edge-operator notation proposed in the issue:
```typescript
breakPoints.slice(1).forEach((_, i) => {
let range: string;
if (i === 0) {
range = `< ${breakPoints[i + 1]}`;
} else if (i === breakPoints.length - 2) {
range = `≥ ${breakPoints[i]}`;
} else {
range = `${breakPoints[i]} - ${breakPoints[i + 1]}`;
}
...
});
```
However, this would also require updating `formatCategoryLabel` in the Legend component since it currently splits on `" - "` to format the numbers. The interval notation (`[1, 81)`) would be more semantically precise and wouldn't require changes to the delimiter-based formatting — you'd just need to ensure the brackets don't get stripped.
The relevant files for a fix are:
1. `superset-frontend/plugins/preset-chart-deckgl/src/utils.ts` — label generation [[6]](https://github.com/apache/superset/blob/829e4d92d91ceae4b43b1ed3b063ffe45377799c/superset-frontend/plugins/legacy-preset-chart-deckgl/src/utils.ts)
2. `superset-frontend/plugins/preset-chart-deckgl/src/CategoricalDeckGLContainer.tsx` — legend rendering [[7]](https://github.com/apache/superset/blob/829e4d92d91ceae4b43b1ed3b063ffe45377799c/superset-frontend/plugins/legacy-preset-chart-deckgl/src/components/Legend.tsx)
3. `superset-frontend/plugins/preset-chart-deckgl/src/layers/Polygon/Polygon.tsx` — where `getBuckets` is called [[8]](https://github.com/apache/superset/blob/829e4d92d91ceae4b43b1ed3b063ffe45377799c/superset-frontend/plugins/legacy-preset-chart-deckgl/src/layers/Polygon/Polygon.tsx)
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