Bayesian Surprise for De-Biasing Thematic Maps.

bayesiansurpriser

Bayesian Surprise for De-Biasing Thematic Maps in R

Overview

bayesiansurpriser implements Bayesian Surprise calculations for thematic maps, inspired by Correll & Heer's "Surprise! Bayesian Weighting for De-Biasing Thematic Maps" (IEEE InfoVis 2016). The default calculation normalizes posterior model probabilities and measures how much each observation updates beliefs about a specified model space.

The package provides seamless integration with:

• sf: Simple Features for spatial data
• ggplot2: Grammar of graphics for visualization
• Temporal/streaming data analysis

Installation

# Install from GitHub (development version)
# install.packages("devtools")
devtools::install_github("dshkol/bayesiansurpriser")

Quick Start

library(bayesiansurpriser)
library(sf)
library(ggplot2)

# Load sample spatial data
nc <- st_read(system.file("shape/nc.shp", package = "sf"), quiet = TRUE)

# Compute Bayesian surprise
result <- surprise(nc, observed = SID74, expected = BIR74)

# View results
print(result)

# Plot with ggplot2
ggplot(result) +
  geom_sf(aes(fill = signed_surprise)) +
  scale_fill_surprise_diverging() +
  labs(title = "Bayesian Surprise: NC SIDS Data") +
  theme_minimal()

Key Features

Five Model Types

1. Uniform Model (bs_model_uniform()): Assumes equiprobable events
2. Base Rate Model (bs_model_baserate()): Compares to expected rates (e.g., population)
3. Gaussian Model (bs_model_gaussian()): Parametric model for outlier detection
4. Sampled Model (bs_model_sampled()): Non-parametric KDE model
5. de Moivre Funnel (bs_model_funnel()): Accounts for sampling variation

sf Integration

# Works directly with sf objects
result <- st_surprise(nc, observed = SID74, expected = BIR74)
plot(result)

ggplot2 Integration

# Custom geom and scales
ggplot(nc) +
  geom_surprise(aes(observed = SID74, expected = BIR74)) +
  scale_fill_surprise()

# Signed surprise with diverging colors
ggplot(nc) +
  geom_surprise(aes(observed = SID74, expected = BIR74), fill_type = "signed") +
  scale_fill_surprise_diverging()

Temporal Analysis

# Compute surprise over time
result <- surprise_temporal(data,
  time_col = year,
  observed = events,
  expected = population
)

# Update with streaming data
result <- update_surprise(result, new_data)

The Problem: Three Biases

Traditional thematic maps suffer from three key biases:

1. Base Rate Bias: Visual prominence dominated by population density
2. Sampling Error Bias: Sparse regions show misleadingly high variability
3. Renormalization Bias: Dynamic scaling suppresses important patterns

Bayesian Surprise can help address these biases by comparing observations against explicit models, such as population base rates and sampling-variation models.

How It Works

The default method uses KL-divergence to measure "surprise":

Surprise = KL(P(M|D) || P(M))
         = Σ P(M_i|D) * log(P(M_i|D) / P(M_i))

Where:

• P(M) = Prior probability of model M
• P(M|D) = Posterior probability after observing data D
• High surprise = data significantly updates our beliefs

The original JavaScript demo associated with the paper used an unnormalized per-region score for some map outputs. This package keeps that behavior only as an explicit legacy comparison option (normalize_posterior = FALSE); new analyses should use the normalized default.

References

Correll, M., & Heer, J. (2017). Surprise! Bayesian Weighting for De-Biasing Thematic Maps. IEEE Transactions on Visualization and Computer Graphics, 23(1), 651-660. https://doi.org/10.1109/TVCG.2016.2598839

License

MIT.