# Overview

Calculating variables on-the-fly is possible with a variety of simple descriptors to derive new fields or use pre-processed data. There are three variable types:

* **Continuous**: Numeric variables on a continuous scale, such as population density or access to internet
* **Categorical**: Ordinal variables with fixed categories for each geography, such as electricity infrastructure, vulnerability category, or any dummy variables.
* **LISA**: *Local Indicator of Spatial Autocorrelation* statistics, which identify significant hotspots, coldspots, and neighboring geographies.

In `map-config.js` in the project root folder, you'll see `variables` where you can define your variables.

```javascript
const variables = [
    {
        variable: "Median age",
        numerator: 'Median age',
        binning: 'naturalBreaks',
        numberOfBins:7,
        colorScale: colors.colorbrewer.Purples
    }
    ...
]
```

In this example, we make a variable called `Median Age` that uses the column `Median Age` from our GeoJSON. It uses the *natural breaks* binning strategy (more on binning [here](https://github.com/nofurtherinformation/webgeoda-gitbook/tree/f32b024ae45448f60ff60d3566f1267e6994e579/data/variables/data/creating-variables/binning-types.md)), with 7 bins, and uses the [ColorBrewer](http://colorbrewer.org/) purples color scheme.

You can declare multiple variables, which will appear in the drop down menu on the left side of the map Each variable can be dynamically binned, or provided with a fixed color scheme. You can use time-series data, single columns, or categorical data.

See the [full variable specification](https://github.com/nofurtherinformation/webgeoda-gitbook/tree/f32b024ae45448f60ff60d3566f1267e6994e579/data/variables/data/variables/full-spec.md) for more information.

## Available Color Scales

Currently, all [ColorBrewer](http://colorbrewer.org/) scales are included. Most support 3-9 bins. See more [here](https://github.com/nofurtherinformation/webgeoda-gitbook/tree/f32b024ae45448f60ff60d3566f1267e6994e579/data/variables/data/variables/colors.md)


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