Understanding Basic Terrain Concepts in 3D Graphics

A beginner-friendly exploration of the core concepts behind 3D terrain rendering in Three.js — understanding heightmaps, vertices, triangles, and how elevation data becomes a real-time 3D mountain mesh in the browser.

Heightmap

A heightmap is data that stores elevation.

Usually it is represented as:

  • grayscale image
  • matrix/array of numbers

Example:

0 0 0
0 8 0
0 0 0

The center area is higher than the surroundings.

A heightmap is not a 3D object yet. It only answers:

How high is this location?

Conceptually:

(x, z) → y

Meaning:

  • x and z determine the horizontal position
  • y is the elevation

Vertex

A vertex is a point in 3D space.

A vertex contains:

  • X position
  • Y position
  • Z position

Example:

(10, 5, 20)

Meaning:

  • x = 10
  • y = 5
  • z = 20

A single vertex is only a point. It does not form a surface yet.

In terrain systems:

  • x and z usually form the ground grid
  • heightmap data modifies the y value

Triangle / Face

A triangle (face) is the simplest possible surface in 3D graphics.

It is formed by connecting 3 vertices.

•
|\
| \
•--•

Modern 3D graphics are built mostly from triangles because:

  • they are mathematically stable
  • always planar
  • efficient for GPUs

Complex objects are simply many small triangles connected together.

Terrain in 3D Graphics

A terrain is essentially:

  • a grid of vertices
  • where each vertex gets elevation from a heightmap
  • then connected into triangles

Pipeline:

Heightmap
→ Vertex elevation
→ Triangles
→ Terrain mesh

A smoother terrain usually means:

  • more vertices
  • more triangles
  • more processing cost

Understanding 3D Model Statistics

Example:

Triangles: 22k
Vertices: 11.1k

Meaning:

  • the model surface is built from ~22,000 triangles
  • the model contains ~11,100 vertices

More triangles generally mean:

  • more detail
  • smoother shape
  • heavier rendering cost

Key Insight

3D terrain is not a “solid mountain”.

It is actually:

many connected triangles shaped by elevation data.