Add an external web link into pupup Form

You can add web link into popup form window.  The popup window show database attributes and appears when a user click on a feature in a map.   

In the previous example, links have been configured in the Form attached to the layer.  The URL link can and should include variable components. A variable component consists of a variable name surrounded by square brackets. The system variables $lat and $lon will be replaced by the feature's latitude and longitude in degrees, respectively. All other names will be replaced by the value of the field of the same name in the feature.  Here's an example of this:

Then by clicking on the link, a user will view the link into a modal view.  The title of the modal view will be the label option in the form configuration.