A core-periphery approach to defining community boundaries

K. Blake Vernon and Scott Ortman

2023-08-29

kbvernon/eaa_2023-community_centers

Boserup cycles

Can explain the behaviors that lead to agriculture.

Challenges for archaeology

  1. Estimating extent of agricultural land
  1. Accommodating interactions at multiple spatial scales
  1. Handling inconsistent site definitions (i.e., lumping v splitting)

Can try regionalizing sites

CBSA Urban Core

Like core-based statistical areas

CBSA Urban Core

Defined by the US Office of Management and Budget.

Inspiration

Kelsey Reese et al (2019) shows that focus should be on commute time!

The algorithm

Step 1: Identify community centers

A community center is a site containing some form of civic architecture or more households than could plausibly be related by kinship.

Step 2: Find nearest farms

‘Nearest’ here refers to least-cost or “commute” distance.

Step 3: Join neighboring community centers

For centers \(C_1\) and \(C_2\) with populations \(N_1 \leq N_2\), if \(pN_1\) are within distance \(D\) of \(C_2\), then \(C_1\) is a neighbor of \(C_2\).

Step 4: Calculate all travel paths

This step ensures communties are “concave” (short paths never leave the community) and helps to avoid unrealistic shapes.

Step 5: Draw community boundary

Uses GEOS ST_ConcaveHull as implemented by sf in R.

Results with VEPII data

Changes in density through time

Log Density: Low Medium High

Changes in density through time

Log Density: Low Medium High

But a smidge a-historical

Area never changes, just density.

Conclusions

WEAKNESSES
1. Lossy method discretizes a continuous process
2. Narrow boundaries are real, but only meaningful in specific contexts
3. Contingent boundaries are identifiable, but only when connection between core and periphery is obvious
STRENGTHS
1. Parsimonious network structure based only on constraints of time and space
2. Grounded justification owing to well-established geographic and statistical theory (namely, Tobler's Law)
3. Unoriginal an analog to CBSA, provides a hybrid of density and distance based clustering algorithms
4. Fruitful provides an empirical estimate of agricultural land area
5. Comparable results may contribute to modern urban and economic geography
6. Concave the shortest path between any two points in a community will never leave that community

Acknowledgments