The establishing shot may be one of the cornerstones in both screenwriting and the finished film product. This shot “establishes” a location or setting, often using an exterior or back up shot to lay out the scene. It gives the entire lay out of the area so people can understand the story space and have a basic idea of what is going on and where.
This is often laid out in the script, yet is rarely actually titled as an establishing shot. To indicate that a certain scene is an establishing shot would be over stepping the bounds of a spec script writer and entering the decision making process of the director. Instead an establishing shot will have a simple heading that will indicate a few elements while making it obvious because of its context that it is an establishing shot.
You have to get three essential things in your heading for an establishing shot. You have to indicate whether or not it is an interior or exterior location, where that location is, and if it is day or night. In some cases you can add more information, but this should usually come in the scene description to follow.
After the heading you go on to describe the establishing shot in a short sentence or two. Since there is not really any action this should not be too long of a description. A longer description can be used for the main scene, but the establishing shot is usually just a clip of a location. Example:
EXT. PHILEDELPHIA – NIGHT
The Philadelphia high rise glows as dusk sets in.
This lays out the minor details of the establishing shot and tells you essentially what you are going to see. It is then up to the director and director of photography to decide exactly how this establishing shot is going to be executed. You should never indicate in the heading or descriptive text that it is an establishing shot. That would be excessive and redundant, making it look less professional to those who will option spec scripts.