Reading the Legend

The color scale bar above the timeline doesn't mean the same thing on every view. SST's range changes when you switch to a different pass or region; chlorophyll's never changes at all. Knowing which is which keeps you from comparing colors across two views that aren't actually on the same scale.

SST: a scale that resets per pass or region

SST's min and max are set from the actual temperature range present in the current pass or region: the pipeline computes it from the 2nd to 98th percentile of valid readings, so a handful of extreme outlier pixels don't stretch the whole scale. That range updates only when you switch to a different pass, source, or region, not while you pan or zoom within the same view. The practical effect: the same shade of orange can mean a different temperature in two different regions, or even in two different passes of the same region on different days. Always check the legend bar for the current range rather than assuming a color you remember from another session.

Chlorophyll: a scale that never changes

Chlorophyll uses a fixed logarithmic scale from 0.01 to 100 mg/m³ that never changes: not by pass, not by region, not by zoom. Concentrations in the real ocean span three orders of magnitude, so a shifting scale the way SST uses would make the same color mean wildly different things from one view to the next. Purple and blue mean very clear water; green is moderate; yellow and red mean nutrient-rich or murky water. Because the scale never moves, a chlorophyll color always means the same concentration everywhere on the map.

Why composites look different zoomed out vs. zoomed in

Composites render two different tile sets depending on zoom level. At the widest zoom levels (roughly z1 to z4) you're looking at global tiles stretched from the whole planet's data. Once you zoom in on a selected region (roughly z5 and beyond), the map switches to regional tiles stretched from just that region's own data, which usually shows more contrast for the water you're actually looking at. The legend number itself always reflects the region-tuned range once you've picked a region, even briefly at the widest zoom before the regional tiles have taken over, so treat the legend as showing you the region's range, not necessarily the exact colors of whatever tile is on screen at that instant.

Collapsing the legend

The legend can be collapsed: look for the palette icon at the end of the timeline. See using the timeline for the rest of the timeline's controls, or finding temperature breaks for how a sharp color transition on this legend actually gets used in the field.