Syria: Mapping the conflictContinue reading the main story
Homs, Syria's third largest city, has been a key battleground in the uprising. It was dubbed the "capital of the revolution" after residents embraced the call to overthrow the president in early 2011 and much of the city fell under the control of the opposition. However, over the past two years government forces have retaken most of the opposition strongholds, laying siege to areas once home to tens of thousands of people and forcing rebel fighters into the Old City.
The capital witnessed major fighting in July and August 2012, but remains mostly under government control. The rebels have strongholds in a number of outer districts. In August 2013, footage emerged of a chemical weapons attack on several Damascus suburbs. Hundreds were killed, according to foreign governments and activists. Both sides blamed each other for the incident.
The town of Qusair, close to both the Lebanese border and the central Syrian city of Homs, is strategically important for both the Syrian rebels and government. Hezbollah, which backs the government, poured in hundreds of fighters in a bid to capture it in June last year. They succeeded, helping Mr Assad's forces regain the upper hand in the conflict.
Fighting broke out in Syria’s largest city in July 2012 with rebels taking control of a number of districts. However their offensive stalled and the battle became a war of attrition, with little movement of front lines. The city remains divided, with opposition forces controlling the east, while the government holds the west. Much of the Old City has been levelled by fighting.
Mapping territorial possession is made more difficult by the tactics employed by the various rebel groups.
They operate as highly mobile guerrilla forces, and when threatened by government troops will not defend territory but rather tactically withdraw with the aim of preventing losses.Conflict origins
The conflict in Syria began after President Bashar al-Assad's government used lethal force to crush pro-democracy demonstrations that erupted in March 2011.
Opposition supporters began to take up arms, first to defend themselves and later to expel security forces from their local areas.
The country soon descended into civil war as armed rebel brigades battled government forces for control of cities, towns and swathes of countryside.
In 2012, rebel forces enjoyed a series of tactical successes that challenged the government's military dominance.
They bounced back from the army's devastating bombardment of the Baba Amr district of Homs at the start of the year by capturing major bases, seizing heavy weaponry, disrupting supply lines, and forcing the army and air force to withdraw from many contested areas.
They also launched co-ordinated offensives on the capital, Damascus, and second city of Aleppo. The rebels eventually took control of several outlying suburbs and towns in the Ghouta agricultural belt around Damascus, and ousted troops from large parts of Aleppo.Current control
However, the advances were not decisive. By the start of 2013, the government had begun to recapture opposition strongholds around the capital, while there was stalemate in Aleppo, with the city firmly divided into rebel and loyalist-controlled sectors.
In June 2013, government troops backed by fighters from the Lebanese Shia Islamist movement, Hezbollah, recaptured the strategically important town of Qusair, close to the Lebanese border.
They then launched assaults on the remaining rebel strongholds in Homs and the Qalamoun mountains, which lie between the border with Lebanon and the key motorway linking Damascus with Homs and the heartland of President Assad's Alawite sect on the Mediterranean coast.
The rebels have also been affected by a deadly conflict since January between jihadists from the Islamic State in Iraq and the Levant (ISIS) and members of Western-backed and Islamist brigades.
The situation on the ground remains very fluid and any analysis will always be based on an assessment of reports of fighting, troop and weapons movements and other incidents.
In 2012, the BBC produced a series of maps based on analysis by the Institute for the Study of War (ISW), a US-based think tank.
The ISW based their work on reports from human rights and opposition activists, as well as from the official Syrian Arab News Agency (Sana) and international journalists.
The map above, produced by the Syria Needs Analysis Project (SNAP), is based on information from the US government compiled from media sources.