Motivation

Motivation

More than 1.2 million people already live in high-pollution zones within 500 feet of a Southern California freeway, with more moving in every day. Between 2000 and 2010 — the most recent period available — the population within 500 feet of a Los Angeles freeway grew 3.9%, compared with a rate of 2.6% citywide.

url

Replication for Riverside County

• goal is to detect which tracts intersect highway buffer
• estimate populations inside buffer
• (exercise 4)

Data

• State highway layer
• Riverside County tracts

Highway Layer [url]

Clipping

Highway Layer [url]

Issue

• We don’t need the entire state network
• Only segments in Riverside County
• Efficient: replicate for all counties
• Divide and conquer

Clipping

• Need a layer that has the clipping polygon
• Apply to segment layer

Clipping polygon

• Dissolve Riverside tracts

Dissolve: Menu

Clipping

Spatial Joins

Spatial Joins

• Add additional attributes to layer based on spatial relations with other layer
• e.g. assign tract poverty rate to houses in each tract (hedonic modeling)
• e.g. dummy variable for tracts intersecting road buffer

Segments and Tracts

• One tract can intersect more than one segment
• Not what we want

Fix: Buffer

• Buffer segments
• Creates polygons

Problem with CRS

Change CRS

Buffer Again

Remember Dissolve?

Next Up

• OpenStreetMap