R Mapping

R Mapping Ecosystem (Meta-Skill)

Overview

This is a meta-skill that helps you choose the right R mapping workflow. The R mapping stack consists of 2 specialized packages that work together.

Install both: install.packages(c("freestiler", "mapgl"))

API keys: Mapbox styles require MAPBOX_PUBLIC_TOKEN; MapLibre works without keys (CARTO/OpenFreeMap)

References

• references/integration-patterns.md - How freestiler and mapgl work together

For per-package API docs, invoke the corresponding package skill (/r-freestiler, /r-mapgl).

When to Use Which Package

REQUIRED: After reading this skill, you MUST invoke the relevant sub-skill (r-freestiler or r-mapgl) before writing any code. If the task involves .pmtiles files, invoke r-freestiler. If the task involves map display, invoke r-mapgl. For pipelines, invoke both.

When NOT to Use

• Simple marker maps (use leaflet)
• Static print maps (use tmap or ggplot2 + sf)
• Quick exploration of small datasets (use tmap_mode("view") or maplibre_view())
• Non-spatial data visualization (use ggplot2)

Key Workflow Decisions

Dataset size determines your path:

Hosting context:

• Static hosting (GitHub Pages, Netlify): freestiler PMTiles → mapgl
• Shiny server: Can use sf directly with mapgl, but consider tiles for large data

Common Integration Patterns

Small Dataset: Direct to Map

library(mapgl)
library(sf)

nc <- st_read(system.file("shape/nc.shp", package = "sf"))

maplibre(style = carto_style("positron")) |>
  fit_bounds(nc) |>
  add_fill_layer(
    id = "counties",
    source = nc,
    fill_color = interpolate(
      column = "BIR74",
      values = c(500, 10000),
      stops = c("lightblue", "darkblue")
    )
  )

Large Dataset: Tile → Map Pipeline

library(freestiler)
library(mapgl)

# Step 1: Create tiles (run once)
freestile(
  input = large_sf,
  output = "tiles.pmtiles",
  layer_name = "features"
)

# Step 2: Serve and visualize
view_tiles("tiles.pmtiles")  # Quick preview

# Or manual control:
serve_tiles(path = dirname("tiles.pmtiles"))
maplibre() |>
  add_pmtiles_source(
    id = "src",
    url = "http://localhost:8080/tiles.pmtiles"
  ) |>
  add_fill_layer(
    source = "src",
    source_layer = "features",  # Must match layer_name
    fill_color = "steelblue"
  )

Memory-Efficient Streaming (10M+ Features)

library(freestiler)
library(duckdb)

# Process without loading into memory
freestile_query(
  query = "SELECT * FROM read_parquet('huge_spatial.parquet')",
  output = "massive.pmtiles",
  layer_name = "points",
  streaming = "always"  # Critical for large datasets
)

Shiny App with Dynamic Filtering

library(shiny)
library(mapgl)

ui <- fluidPage(
  selectInput("year", "Year", choices = 2010:2020),
  maplibreOutput("map", height = "600px")
)

server <- function(input, output, session) {
  output$map <- renderMaplibre({
    maplibre(style = carto_style("positron")) |>
      add_pmtiles_source(id = "data", url = "tiles.pmtiles") |>
      add_circle_layer(
        id = "points",
        source = "data",
        source_layer = "features"
      )
  })

  observeEvent(input$year, {
    maplibre_proxy("map") |>
      set_filter(
        "points",
        list("==", list("get", "year"), input$year)
      )
  })
}

Decision Tree

Start: Need to map spatial data
├─ <10k features?
│  └─ YES → Use mapgl directly with sf source
├─ 10k-1M features?
│  └─ YES → freestiler (default settings) → mapgl
├─ >1M features OR >500MB file?
│  └─ YES → freestiler with streaming → mapgl
└─ Need static hosting?
   └─ YES → freestiler PMTiles → mapgl (no server needed)

Critical Integration Points

1. CRS must match: Transform to WGS84 before tiling: st_transform(data, 4326)
2. Layer names must align: layer_name in freestiler = source_layer in mapgl
3. Server for local development: Use view_tiles() for quick preview, or serve_tiles() + mapgl for custom control
4. File paths: PMTiles can use file:// URLs with absolute paths in mapgl

Common Mistakes

1. Wrong workflow order: Don't tile small datasets; don't pass huge sf objects to mapgl
2. Missing streaming flag: Add streaming = "always" for datasets >10M features
3. Layer name mismatch: freestile(layer_name = "x") requires add_*_layer(source_layer = "x")
4. Server requirements: Python's http.server doesn't support PMTiles; use Node's http-server or freestiler's built-in server
5. CRS assumptions: Always verify and transform to EPSG:4326

Advanced

See references/ for:

• integration-patterns.md: Production workflows, Shiny patterns, multi-layer maps, troubleshooting

For package-specific documentation, invoke the individual skills:

• r-freestiler: Tile generation, SQL queries, zoom strategies
• r-mapgl: Layer styling, Shiny integration, 3D terrain, interactive controls