Mapping Basics

Point or Node 

A Point or Node on a map represents the smallest object, often part of an area or path. Special Points, like a tree or cafe in such case it is called as Points of Interest (POI) with tags for information. Each point has unique Latitude and Longitude coordinates. 

Lines or Ways 

Only points or nodes are not sufficient to describe information on maps. More complex objects like roads, rivers, boundaries are shown using Ways (lines or paths). Ways are the lines connected by nodes. Way is an ordered list of nodes. 

Areas 

Apart from Points and Ways, there are Areas like Buildings, Parks, Playgrounds, Lakes on the map. They are represented by closed ways. Thus, when first and the last node of a way coincide, we get an Area. 

Relation 

Although Point, Line and Area represent most of the objects on map, a few objects on map need a special type of element such as Relation to describe them. Relation is a combination of one or more of the basic elements viz point, line, area.  

Tagging 

Tag in OSM is a kind of label which describes the geographical object on map in a uniform way. Tag is always given as key-value pair. Key represents specific feature and Value is the proper description of the feature. Only ASCII and lower-case characters are used in keys. Underscore ( _ ) is used for space.