When using the term "feature" in GIS, what is often (if not always) meant is a geographical feature which "is a representation of real world phenomenon associated with a location relative to the Earth" (ISO 19125-2:2004). Are there non-geographical features and if so, are there any examples of such?
For example, could a compass or a scale bar be considered non-geographical features?
Features in the most general sense are analagous to records in computer science:
In computer science, records (also called tuples, structs, or compound data) are among the simplest data structures. A record is a value that contains other values, typically in fixed number and sequence and typically indexed by names. The elements of records are usually called fields or members.
So a record can be said to have "attributes", e.g. the records in an "attribute table". One of these attributes may be a spatial data structure describing the geographic (or non-geographic -- not every feature has to exist in the real world) coordinates of the entity represented by the record.
In a GIS, often a distinction is made that a feature represents a spatially-enabled record, however this is not always the case.
For example, in FME (the "Feature Manipulation Engine" by Safe Software), features may be spatial or non-spatial. Indeed, you will very often be working with non-spatial features in that environment, e.g. the rows of a CSV file would be considered features.
Regarding your examples of a compass or scale bar, yes, I think these could be considered non-geographical features, because they don't represent real world entities, but they are themselves entities. I would suggest that they are cartographic features, since they represent distances or directions on a map. As such they are features of a map, not features of the Earth. In another sense, one could argue that digital versions of these elements are indeed records in the computer memory/data structures that make up a map; for example in ArcGIS, these might be represented by elements on a page layout, and when you save the map, these records are persisted in structured storage in the form of a map document (MXD) file.
According to the "OpenGIS Implementation Specification for Geographic information - Simple feature access - Part 1" (see http://www.opengeospatial.org/standards/sfa ) #4.11 a feature is an "abstraction of real world phenomena. (...) [adapted from ISO 19101]". This backs up the definition of "feature" by SS_Rebelious.
In order to avoid unwanted semantical constraints I prefer to say, that "a feature is an object - like in OO programming - which is an instance of a class, and has (in addition) at least one geometry attribute, which includes a dimension (2D/3D) and a coordinate reference system associated to it."
So a "non-geographical feature", to me, is just an object with no geometry attribute (value).
P.S. I would strictly distinguish "feature (or feature instance)" and "feature type (or feature class)", like "object" and "class" in mainstream IT, like in the OGC "Simple Feaurre Spec." mentioned above.
To my mind the definition of geographical future as
a representation of real world phenomenon associated with a location relative to the Earth
is not quite correct. If we speculate about 'geographical future' we mean a feature that is the subject of study of the Geography. And a better explanation for the term can be found here:
Geographical features are the components of the Earth. There are two types of geographical features, namely natural geographical features and artificial geographical features. Natural geographical features include but are not limited to landforms and ecosystems. For example, terrain types, bodies of water, natural units (consisting of all plants, animals and micro-organisms in an area functioning together with all of the non-living physical factors of the environment) are natural geographical features. Meanwhile, human settlements, engineered constructs, etc. are types of artificial geographical features.
Notice that in this case geographical feature is a consistent phenomenon (and consistency is present as an attribute for 'geographical feature' in Russian definition of this term)
See, if we will use the definition you quoted - a vehicle with the GPS tracking enabled would be valid geographical feature. But from geographical point of view a single moving vehicle is not a valid geographical feature. For Geography in this case only a spatial distribution of vehicles (e.g. aggregated information) may be a valid geographical feature.
So from geographical point of view a single vehicle (or a flock of birds) is a non-geographical feature. A compass and a scale bar on a map are just a map decorations and may not be considered as geographical or non-geographical features because they are not a real world objects.
EDIT: I see that many people have issues in distinguishing geographical and non-geographical features. It is completely Ok due to scientists have the same issues too))) I was asked to provide additional references to my statements. Unfortunately I have only Russian sources to refer to. There is one of my favourite books: А.Г. Исаченко "Теория и методология географической науки", 2004 (A.G. Isachenko 'Theory and Methodology of the Geography Science') ISBN 5-7695-1693-3. He discuss the term 'geographical feature' at page 27. He states that there is a mix of narrow-minded and scientific approaches to determination of 'geographical feature' definition. He continues that there is no pure scientific definition for 'geographic feature' term. Also he notes that identification of any object on Earth as a 'geographical feature' possible only from ultra-chorological point of view.
Conclusion: there is no clear scientific definition of what is 'geographical feature'. But identification of any object that can be mapped (especially if the map won't be representative few moments later) as a 'geographical future' are allowed only for minority of geographers who shares ultra-chorological point of view (and I have'n seen one of them despite I know many geographers) or for persons who are not familiar with the theory of Geography.
