Scoring the Shoreline: How We Calculate Beach Accessibility from Space

Public beaches belong to everyone, but public access is shrinking daily. Creeping privatization, aggressive commercial vendor setups, restrictive municipal parking ordinances, and locked easements make it harder than ever to find a place to lay down a towel. At the Open Sands Index (OSI), we decided that the first step to reclaiming the shoreline is measuring it.

But how do you calculate a standardized metric representing something as complex and legally ambiguous as "beach accessibility"? The answer lies in combining GIS spatial mathematics, automated satellite imagery pipelines, and crowdsourced observation data into a unified, dynamic score from 0 to 100.

The Composite OSI Metric

The Open Sands Index evaluates beachfront parcels using a composite metric divided into four core scoring categories:

1. Regulatory Access (40% weight): This looks at local laws and land-use restrictions. Does the municipality restrict parking to residents only? Are public easements spaced at legal intervals? We ingest local zoning data and parcel deeds to evaluate how legally welcoming a beach is to visitors who do not own beachfront property.

2. Geospatial and Physical Barriers (30% weight): Having a legal right to access a beach does not matter if a massive cliff or private estate blocks the way. We calculate spatial proximity using GIS coordinate paths, computing the walking distance from the nearest public parking space or transit stop to the wet sand. Parcels requiring a mile-long detour score significantly lower than those with direct stairs.

3. Commercial Monopolization (20% weight): This is where satellite imagery and machine learning come in. Commercial beach clubs and hotels frequently set up "ghost chairs"—dozens of empty rental loungers and umbrellas spread across public dry sand to discourage non-paying visitors. Our automated pipeline processes high-resolution satellite passes to calculate the percentage of public dry sand covered by commercial structures during peak hours.

4. Crowdsourced Integrity (10% weight): Ground truth requires human eyes. Through the OSI PWA, visitors report real-time accessibility status, such as hostile "Private Beach" signs posted on public sand, aggressive security guards, or broken public stairs. These reports are filtered for anomalies and factored directly into the active score.

Processing Spatial Data at Scale

Calculating physical proximity for thousands of miles of coastline is computationally expensive. Our engineering stack leverages Mapbox and specialized GIS tooling to compute buffer shapes along the shoreline. We segment the US coastline into 50-meter parcels. For each segment, the platform performs a fast spatial query, finding the shortest navigable path from a public road to the median high-water line.

By compiling these layers, we expose a simple, interactive map overlay that shifts from deep sky blue (fully accessible, free parking, clear easements) to warnings of orange and red (privatized, gated, or heavily monopolized).

Transparency as Advocacy

We believe that code can be a powerful form of advocacy. By publishing our scoring methodology and open-sourcing our dataset, we empower local beachgoers, environmental journalists, and coastal commissions with concrete data. In the fight to preserve the public shoreline, transparency is our greatest tool.