Reading the Map

Click or tap anywhere on the colored ocean for an instant exact reading. SST shows temperature in both °C and °F; chlorophyll shows concentration in mg/m³ plus an estimated water visibility (Secchi depth). Both readouts load instantly, with no server round-trip.

Why the readout is instant

The tile image you see is only the colored picture. Behind it, the map prefetches a value grid (a compact array of the actual numeric readings for the region) as soon as a pass or composite loads. Clicking or hovering reads straight from that grid already sitting in your browser, not the tile image, which is why the number appears with no delay.

How the lookup works

The map checks the finer regional value grid first. If your click falls outside that region's coverage area, it falls back to a coarser global grid (about 0.25°, roughly 25km) so you still get a reading anywhere on Earth. If a point falls inside the regional grid but that specific pixel has no usable reading (cloud, land, or a genuine coverage gap), the map tells you so directly rather than silently falling back; see why there are holes for what that label means. Only a point that misses both grids entirely shows a plain "No data."

Desktop vs. mobile

On desktop, hover to see a live readout that follows your cursor as you move it. On mobile, there's no hover: tap to pin a readout popup at that point instead.

Panning and zooming

Drag to pan, scroll to zoom (or pinch on mobile). The dark navy background is ocean with no data; colored areas show where satellite data is available for the current pass or composite. For how the colors themselves are scaled, see reading the legend. For finding the sharp color transitions worth acting on, see finding temperature breaks, or check Southern California's region page for a worked example.