WHAT IT SHOWS: This chart combines maps of Baghdad's ethnic neighborhoods with density plots of ethno-sectarian killings to show that violence has declined significantly from December 2006 to last month.
ANALYSIS: Hidden beneath many of the density plots are colors that show a major reshaping of Baghdad, from an ethnically mixed city to a patchwork of rival ethnic and religious enclaves whose residents rarely intersect outside their gated communities.
Many analysts, including in the U.S. government, believe that this de facto division of Baghdad -- as opposed to brilliant U.S. counterinsurgency work -- is largely responsible for the decline in violence.
"The polar ization of communities is most evident in Baghdad, where the Shia are a clear majority in more than half of all neighborhoods and Sunni areas have become surrounded by predominately Shia districts," said the National Intelligence Estimate on Iraq last year. "Where population displacements have led to significant sectarian separation, conflict levels have diminished to some extent."
Many experts say that a more reliable indicator of the country's safety is the flow of refugees and internally displaced people, because if people feel secure, they return home. On that score, the situation in Iraq remains deeply troubled.
The U.N. High Commissioner of Refugees estimates that beyond the more than 2 million refugees who have fled to other countries, there are another 2.8 million Iraqis who are internally displaced, out of a population of 26 million. More than 1 million have no regular income; 300,000 have no access to clean water.
U.N. and U.S. officials have urged refugees and other displaced people not to try to return home precisely because Baghdad has become so balkanized. Officials fear that tensions and violence will erupt again if people try to reclaim their homes in once mixed neighborhoods.
-- Glenn Kessler