For OpenStreetMap as well as for the Overpass API, a couple of notions are explained.
Areas are a special type of object within the Overpass API. The areas are not part of the OpenStreetMap data opposed to nodes, ways, and relations, but are generated by Overpass API. These are a workaround, because areas are used in OpenStreetMap as a concept, but there is no proper data type for them.
A bounding box is defined by two values for a latitude and two values for a longitude. It consists of all coordinates that have a latitude that is between the two supplied latitude values and that have a longitude that is between the two supplied longitude values.
Deriveds are a special type of object within the Overpass API. The deriveds are not part of the OpenStreetMap data opposed to nodes, ways, and relations, but are generated during the runtime of a request. Using deriveds makes it possible to rewrite tags and to simplify geometries.
This is one of the building blocks of a request. An evaluator is called in the context of a statement, block statement, or the special filter if. Depending on its type, it either operates on the whole set of objects chosen in a variable or individually on each object. Again, depending on its type, it returns a number, a string, or a geometry.
This is one of the building blocks of a request. A filter always belongs to a query statement and filters for the objects to be selected there. The multiple filters of a query statement are connected by conjunction, i.e. there are always found only those objects that match all filters of the respective query statement.
A key is a part of a tag. It is the leading string.
A specific type of object in the data model of OpenStreetMap. It represents a single coordinate. With tags it is a distinguishable object, without tags it almost always is just a part of a way to equip it with coordinates.
The text in the formal query language that the client (e.g. from the front-end Overpass Turbo) sends to the server. The content of the request exclusively controls what out of the OpenStreetMap data is fetched.
A specific type of object in the data model of OpenStreetMap. It models all things that are beyond the scope of nodes and ways.
See at Variable
This is one of the building blocks of a request. Statements are those parts that can be independently executed. Statements can be classified as block statements or simple statements. The two most important statements are query to select objects from the OpenStreetMap database and print to append selected objects to the response.
A tag is a data structure in both OpenStreetMap and the Overpass API to store textual data. Every tag consists of a key and a value and is part of an object, i.e. a node, a way, a relation or a derived.
A key is a part of a tag. It is the trailing string.
A variable in the Overpass API is always a set variable. Set variables serve during the execution of a request to convey object selections from statement to statement.
A specific type of object in the data model of OpenStreetMap. It represents a polyline. If the polyline is closed, then it can be an area.
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