Points, Lines, & Planes


A point is an exact location in space. It has no size, only position. To show you this location, we are marking a point on the paper. This is just a model of a point.

To prevent points from being confused with one another and to ensure everyone understands which point we are referring to, points are named using uppercase letters.

We use points to refer to, or name, the center of a circle, the beginning or end of a line segment, the intersection points of two lines, or the vertices of polygons.

Lines ( Line - Line Segment - Ray )

Line Segment 

The shortest distance between two points. A segment, part, or piece of a line.


We represent it as AB
 For a line segment with endpoints A and B, you might represent the length of the segment as:

eg ;  I AB I = 5 cm 

In geometry, when we refer to a line, we actually mean a line segment.


Arrows indicate that the line goes on infinitely.

You can also represent it this way.This time, you need to write the letter in lowercase; our shape indicates line d.

A line is a straight one-dimensional figure that has no thickness and extends infinitely in both directions. It is defined by an infinite set of points that lie along the same path, equidistant from each other, and it goes on without end in both directions. 


A "ray" in geometry is a part of a line that begins at a particular point and extends infinitely in one direction. 
It's often used in the context of angles, where it can define the sides of an angle with a common endpoint called the vertex.


A plane is an imaginary flat surface that has length and width but no thickness and goes on forever.

Imagine a thin veil over your classroom, and think of this veil extending beyond your classroom, the mountains and hills, out of the world, and on forever. This is a plane.

In the real world, there are no planes. When we draw something on a flat piece of paper, we are drawing on a piece/part/segment of a plane, except that the paper itself is not a plane because it has thickness!

Imagine a virtual, thickness-less screen protector on your computer screen; this is a piece of a plane.

We usually use a parallelogram to represent a plane, but of course, what you see is not a real plane; it's just a drawn model to show you. We give it a name with a capital letter; in the figure, you are seeing plane P.

Why are planes so important?

Planes are one of the basic undefined terms in geometry, along with points and lines. They form the foundation upon which all other geometric concepts are built.

All the geometry you learn in schools, such as points, lines, distances, angles, polygons, shapes exct is formed in a plane.

The upper surface ABCD and the lower surface EFGH are parallel to each other, The right or left surface intersects with the upper or lower surface.

What is next ?

Lines and Angles

Geometry Index