Being in a wheelchair should not restrict where you can safely go. While you may have some issues in natural terrain, navigating an urban area should not be a problem.
However, you likely know that is not true. There is a range of hazards that could cause you harm. The Federal Highway Administration explains a few things you should watch out for when using sidewalks in a wheelchair.
A sidewalk should be continuous and free of any barriers. It also should have lowered edge areas where you can access it from another area, such as the pavement or grass. There should be nothing that encroaches on the sidewalk, such as trees or bushes, that would make it so you cannot use it properly and have to go off the edge or even leave the sidewalk to go around.
Sidewalks need to be free from cracks and holes. They should be even and smooth. Any unevenness is a huge hazard. This includes unevenness that comes from a design flaw. Safe sidewalks are flat.
Beyond bad leveling issues, design problems may include sidewalks that are too winding or too narrow. Another design issue is putting them in an area where they will sink without proper foundation preparation. Steep grades are also an issue. Designers should avoid them whenever possible.
If there are certain conditions or design issues that nobody can fix or that they cannot fix right away, there should at the very least be posted warnings and barriers that alert you to the issue.
If you see an issue, alert the appropriate person or authority to get it fixed as soon as possible. Not only will that ensure you do not become a victim of an accident but it also safeguards everyone else who uses that sidewalk.