Introduction to editing in OpenStreetMap
Anybody can edit data in OpenStreetMap. This chapter will give you the concepts you need to understand in order to begin contributing.
OpenStreetMap consists of a few basic types of data: nodes, ways, relations, and tags.
A node is a single point with a latitude and longitude. A single node can be a point of interest such as a tree or a mailbox or a place such as a city of a village.
A way is a line. Lines are made by connecting many nodes together. A way can be something like a road or a trail.
An area is a way where the starting and ending point are the same. Note that not all closed ways are always areas. There might be a circular road for an example, which would be a closed way but not an area. A lake, on the other hand, would be an area. Other words for an area include a shape or a polygon. Other examples of an area include a building, a sports field, or a forest.
Relations are used to group geographically-related objects together. Relations are perhaps harder to understand than the previous concepts, but you are also less likely to need them when starting on your path (or way!) as a OpenStreetMap contributor. Relations could be used to group something like the roads of a bus route together. So in the bus route example instead of drawing a new set of ways to describe the bus route you can say which roads are part of the bus route using a relation.
A tag is a key/value pair that is used to describe an object. The key tells you what kind of object it is, for example an amenity or a highway. You then use the value to describe what type of object it is, for example an amenity might be a bank or a pharmacy, while a highway might be a primary road or residential street. There are many tags already use in OpenStreetMap, but there is flexibility to create new ones in case you want to map something nobody else has mapped before. This versatility means you can add any keys and values that you think are needed. Many editors however have presets for common key/value pairs, which makes it easier and faster to edit maps.
Changesets are sets of edits within OpenStreetMap. When you edit OpenStreetMap the changes you make during that editing session are saved in a changeset. This changeset is seen in history tab of the map, and are associated with your user account.