I have two maps within the map composer in qgis. Whenever I want to update one map it updates both maps. How can I prevent QGIS from updating the other map?
On the map item go to 'Item Properties > Layers'. There are two check boxes:
"Lock Layers" = prevent any layers being added or removed from the map window
"Lock styles for layers" = prevents styles changing on layers visible in the map window.
Checking both of these for a particular map item stop any changes happening to that map so you freely make changes to a different map window.