Deterministic Spatial Analysis

Dimensions of vector geometries

• Point: 0-dimension
• Line: 1-dimensional (length)
• Polygon: 2-dimensional (area)

Spatial Relations

Dimensionally Extended nine-Intersection Mode (DE-9IM)

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Food Deserts url

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Today: Clinic Deserts

Buffers and Buffering

Buffers

Buffers (Variable)

Buffers (Rings)

Buffers (Dissolve)

Buffering the Clinics

• food deserts: 0.5 mile distance
• use for the clinic points
• will revisit other distances later

.5 mile clinic buffer

buffer menu

buffer result

buffer result: geometry

buffer rename

Buffering

Using the Buffers for Locational Analysis

• Find what tracts intersect with the buffers
• Create layer with these tracts
• Use: Select by Location

Processing: Select by Location

Processing: Select by Location Dialog

What tracts intersect with the .5 mile buffers?

Save Layer

Saved Layer

Health Deserts

Traditional Approach

• Tracts not intersecting buffers
• Add up population in desert polygons

Identifying Clinic Desert Tracts

Clinic Desert

Clinic Desert Layer

What is the population residing in Clinic Desert?

Desert Tracts Tables

Basic Statistics for Fields

Basic Statistics for Fields: Dialog

Basic Statistics for Fields: Results

Basic Statistics for Fields: File

Basic Statistics for Fields: File

Total County Tract Population

Population Estimates

• County Total: 2,189,641
• In Clinic Desert Tracts: 1,881,643
• In Buffer Tracts: 307,998
• Population with access problems: 1,881,643

Issues in measuring access to clinics

• all individuals in the tracts intersecting the buffers are in the buffer
• overestimation of people within .5 miles of a clinic
• underestimation of people in the clinic desert

Why overestimation of buffer population?

We can do better

Buffer Tracts

Random Points

Random Points Generated

Random Points Layer

Random Points Layer Symbology

Random Points Layer

Count points in buffers: Layers

Count points in buffers

Points in polygons

Count Field

Count Summary

Count Table

Revised Estimates

• County Total: 2,189,641
• In Clinic Desert Tracts: 1,881,643
• In Buffer Tracts: 307,998
  • 90,630 in buffer, in tract
  • 217,358 out of buffer, in tract
• Population with access problems: 2,099,011
• Population within .5 miles of clinic: 90,630

Issue

• double counting
• points contained in more than a single buffer are counted more than once

Overlapping Buffers

Count Table With Overlapping Buffers

Fix

• dissolve on buffering

Buffer and Dissolve

Dissolved Buffer

New Buffer

New Buffer Feature Count

Points in Polygon Count

Population within .5 Miles of a Clinic

Revised Estimates

• County Total: 2,189,641
• In Clinic Desert Tracts: 1,881,643
• In Buffer Tracts: 307,998
  • 50,190 in buffer, in tract (no double counting)
  • 257,808 out of buffer, in tract
• Population with access problems: 2,139,451
• Population within .5 miles of clinic: 50,190

Next Up

• Vector Analysis: Clipping and Spatial Joins