CSL Map View Web viewer
Drop your .cslmap file on this page to generate a view.
This Web interface does not understand compressed cslmap files: make sure to decompress files (or save them uncompressed) before you try to use them. Merely double-clicking them should suffice.
On macOS, you can find the .cslmap files at ~/Library/Application Support/Steam/steamapps/common/Cities_Skylines/CSLMapView. You can easily access that folder through the Finder by hitting ⇧⌘G and pasting that path into the dialog box.