WASHINGTON — The map of closed American embassies — and those that remain open — in the Middle East and Africa provides a window into the Obama administration’s concern about a potentially imminent al-Qaida terrorist attack on overseas U.S. interests.

While diplomatic missions across a broad swath of the Arab world are affected, some, including in capitals that have been targets for extremists in the past, are not.

And those chosen for closure in Africa and the Indian Ocean suggest that the fear may be as much about the vulnerability of certain embassies and staff and the range of increasingly mobile terrorists as it is about specific threats.

One apparently key factor: How significant is the security that is now in place?

A total of 19 U.S. embassies and consulates in 16 countries have been ordered to close to the public until Saturday. They run along a jagged, east-to-south crescent from Libya through the Persian Gulf to Rwanda and include the island nations of Madagascar and Mauritius. That’s fewer missions in fewer nations than were ordered closed this past Sunday in the administration’s initial response to intelligence that al-Qaida in the Arabian Peninsula was gearing up for an attack.

The changes, coupled with the inclusions and omissions, show how the threat analysis has evolved.

President Barack Obama, in his first public comments on the matter, said the terror threat is “significant enough that we’re taking every precaution.” Despite the global travel warning, he said Americans should not cancel their overseas travel plans but should “show some common sense.”

According to the State Department, the closures are all the result of the same intelligence on the threat. Yet, that intelligence stream appears to be significantly diffuse, covering embassies and other posts stretching 4,800 miles from Tripoli, Libya, to Port Louis, Mauritius, and not limited to Muslim or Muslim-majority nations.