The coronavirus outbreak in the US continues to grow. So far, more than 40,000 cases have been confirmed across all 50 states, and at least 550 Americans have died.

Testing is a key part of fighting a pandemic — knowing the extent of an outbreak and how quickly it's spreading is an essential piece of information for policymakers, healthcare providers, and the public. After weeks of delays in ramping up its testing, the US is now beginning to roll out testing on a much larger scale. More than 290,000 Americans have been tested for the coronavirus, up from just 10,000 on March 12.

The COVID Tracking Project, a test-tracking resource from two journalists at The Atlantic and the founder of a medical-data startup, publishes frequently updated estimates of the number of tests for the novel coronavirus performed in each state. The project assembles data from state- and local-level public health sources to try to construct the best real-time picture possible of different states' testing systems.

The following map shows how many coronavirus tests each state has done in total since the beginning of the crisis, per 1 million residents (Population estimates come from the Census Bureau.) The data shows that two states with large outbreaks — Washington and New York — have tested the highest shares of their populations.

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Business Insider/Andy Kiersz, data from The COVID Tracking Project

These figures are changing quickly as states continue to ramp up their coronavirus testing capabilities. New York State has drastically increased its testing in the last several days, with the total number of tests performed in the state nearly tripling since last Thursday, according to the COVID Tracking Project's count.

The interactive map below shows where cases are distributed throughout the US:

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