The sidewalk:left=* key can be used to indicate the presence or absence of a sidewalk (pavement/footway/foopath) alongside the left side of the street where the footway runs parallel to the carriageway.
It is usually paired with sidewalk:right=*, and is used where sidewalk=* does not suffice. See sidewalk=* for more information and other useful tagging combinations.
|There is no sidewalk on this side of the road.
|There is a sidewalk on this side of the road, and it is not mapped as a separate way.
|There is a sidewalk on this side of the road, and it is mapped using a separate way.
Concerns for data consumers
sidewalk:left=* overrides the value set by sidewalk=* for the left side of the road, although mixing these is discouraged. sidewalk:left=none should be treated as synonymous with sidewalk:left=no.