Pop-ups bring to life the attributes associated with each feature layer in the map, such as hiking trails, land values, or unemployment rates. They display images and charts, and can link to external web pages.
The default pop-up appearance for a layer—if the layer owner has not configured it for you—is a plain list of attributes and values. The layer owner can save a new configuration, which is why the pop-ups in your map can look good with no effort on your part.
Within a particular map, the map owner can reconfigure the pop-ups to their liking. Map authors define the list of visible and hidden fields and how the information is presented. For example, they might show a simple list of attributes, or provide a rich interactive experience using custom-formatted text, charts, images, and other media.
Information for pop-ups comes from three main types of feature layers: map notes, web layers, and data imported from a file.
To learn more about designing and configuring pop-ups, see Configure pop-ups.