Introduction

This tutorial describes two measures of inequality available in UrbanSim (the Lorenz curve and Gini coefficient), and how to generate them using the Opus indicator maker.

The Lorenz curve indicator in available in UrbanSim as a visual representation of the distribution of a non-aggregate variable over the population. It is used to examine the fairness with which impacts (benefits and costs) are distributed in a given scenario. The Lorenz curve is a graph which represents the cumulative distribution function of a probability function over a population. It is commonly used in the analysis of inequality. The Lorenz curve allows flexible analysis of equity because it is not limited to a specific type of population or variable that is distributed among that population. The Gini coefficient is another way to measure equity, and is derived from the Lorenz curve.

Flexible equity analysis is important for many reasons.

1. There are different ways to look at equity, such as fairness or social justice.
2. There are different ways to categorize people for equity analysis, including location, age, income, family status, pedestrians, etc.
3. There are different ways to measure an impact on a group. For example noise, pollution, land value, income and access to transportation can all be affected by a policy.
4. There are different types of equity, and they can overlap and conflict with one another. For example a policy that ensures fairness (everyone is treated the same) may not take into account that different groups have different needs.
5. Stakeholders' values can vary and change with time.

This tutorial covers creating an indicator with a Lorenz curve selected as the visual output. The specific properties of the Lorenz curve and the Gini coefficient are discussed as well as their common applications and limitations.