diff --git a/docs/core_classes/vec.md b/docs/core_classes/vec.md
index 5cb6a218..d1417f8e 100644
--- a/docs/core_classes/vec.md
+++ b/docs/core_classes/vec.md
@@ -17,7 +17,7 @@ morph::vec<int, 4> v1 = { 1, 2, 3, 4 };
 but you can do maths:
 
 ```c++
-morph::vec<int, 4> v1 = { 1, 2, 3, 4 };
+morph::vec<int, 4> v2 = { 1, 2, 3, 4 };
 morph::vec<int, 4> v3 = v1 + v2; // element-wise addition
 ```
 
diff --git a/docs/visual/index.md b/docs/visual/index.md
new file mode 100644
index 00000000..8ffd9dc3
--- /dev/null
+++ b/docs/visual/index.md
@@ -0,0 +1,6 @@
+---
+title: The visual scene
+layout: page
+permalink: /visual/
+---
+morphologica has a class called `morph::Visual`  which sets up a graphical 'scene'. In
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diff --git a/docs/visual/viz.md b/docs/visual/viz.md
new file mode 100644
index 00000000..7d5746eb
--- /dev/null
+++ b/docs/visual/viz.md
@@ -0,0 +1,10 @@
+---
+title: Visualization with OpenGL
+layout: page
+permalink: /viz/
+---
+morphologica uses OpenGL to draw graphics and text. In a way it's like a game engine for data visualization. Unlike a game engine, it uses very simple shaders and very simple graphics. Where a game would take artist-generated 3D models and render and animate these models, morphologica draws very primitive models out of triangles, which are generated at runtime. For example, to draw a hexagonal grid, it simply creates vertices at the corners of each hexagon, and a vertex in the centre of each hex, then renders lots of triangles. Each group of vertices forms an 'OpenGL model'.
+
+Before it can draw OpenGL models, morphologica needs an OpenGL context to have been set up. morphologica has a class called `morph::Visual`  which sets up a graphical 'scene' and deals with the OpenGL context. By default, morph::Visual uses the library GLFW3 to create a Window and an associated OpenGL context for all the drawing (if you want two windows in your program, you'll need two morph::Visuals).
+
+Within your scene, you will then create one or more instances of a `morph::VisualModel`. This is the base class for a number of different classes that draw different kinds of objects. If you have a custom visualization need, you can derive your own class from  `morph::VisualModel`.
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