How to open a mobile device’s map app when a user clicks on a link?

You can use the GEO URI Scheme “geo:latitude,longitude” specified by RFC 5870 in a link such as

<a href="geo:124.028582,-29.201930" target="_blank">Click here for map</a>

There’s also the comgooglemaps:, which launches the Google Maps app for iOS, for example:

comgooglemaps://?center=40.765819,-73.975866&zoom=14&views=traffic

Where

• center: This is the map viewport center point. Formatted as a comma separated string of latitude,longitude.
• mapmode: Sets the kind of map shown. Can be set to: standard or streetview. If not specified, the current application settings will be used.
• views: Turns specific views on/off. Can be set to: satellite, traffic, or transit. Multiple values can be set using a comma-separator. If the parameter is specified with no value, then it will clear all views.
• zoom: Specifies the zoom level of the map.

And as techtheatre said, you can use a regular Apple Maps link to trigger Apple Maps:

//maps.apple.com/?q=Raleigh,NC

Leaving off the protocol will automatically select the correct one to use, so if you wanted to have a dynamic link you could just create some conditional code that changes the link between google.com and apple.com depending on which system you’re on.