Classlist's Parent Map feature works on a two-way system, this means that your location on the map can only be seen by other parents who are also visible. This keeps the system fair, but does mean that an address must be provided to use the feature. This can be done at account creation, or through your profile (more information on managing your profile can be found here).
Simply enter your details into the box and tick the 'Opt in' box. Classlist's Terms of Service can be found by clicking the link provided, or they can be accessed here.
Make sure you hit the 'Save' button to confirm any changes.
If the problem persists, you should also consider trying to open the page using a different browser. NB When using Classlist on Internet Explorer 11, the feature will often not appear at all.
Please contact your Class Admin or firstname.lastname@example.org if you're still unable to view the map having tried the approaches above.