Create an Ordinal Scale

PIE.md

@@ -33,3 +33,23 @@ var dataset = [
     { label: 'Dijkstra', count: 40 }
 ];
 ```
+
+## Create an Ordinal Scale
+
+An ordinal scale maps discrete values (can't be interpolated) to discrete values.
+
+```javascript
+var mapper = d3.scaleOrdinal();
+mapper.range([45, 63, 400]);
+mapper.domain(['Bob', 'Sally', 'Zagthor']);
+
+console.log(mapper('Bob'));
+console.log(mapper('Sally'));
+console.log(mapper('Zagthor'));
+```
+
+You cannot invert ordinal scales:
+
+```javascript
+console.log(mapper.invert(45));
+```