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GIS Watersheds

Brian S. Yandell

10 August 2026

gis.Rmd

This document details the spatial integration of simulation grids with geographic features, spatial polygon overlays (add_watershed_hex_overlay), Moose habitat suitability scoring, and the separation of interactive Leaflet GIS discovery into the standalone hexmap package.

1. Spatial Hexagonal Substrate Grid & Habitat Overlays

The ewing package provides an offline-capable spatial substrate engine that constructs continuous hexagonal grid meshes across custom landscapes (such as Isle Royale).

1. Hexagonal Mesh Generation & Autoplotting

  • create_isle_royale_hex_overlay(hex_diameter): Builds an S3 spatial substrate mesh (watershed_hex_overlay) across the Isle Royale boundary, reading pre-computed .rds layers from inst/extdata/isle_royale/.
  • add_habitat_hex_overlay(hex_obj): Intersects habitat features (lakes, waterways, bogs, forests) with hex cells, assigning habitat suitability scores and movement weights.
  • autoplot.watershed_hex_overlay() & autoplot.habitat_hex_overlay(): Generates static ggplot2 autoplots of the hexagonal substrate mesh and habitat suitability overlays.

2. Decoupled Interactive Mapping: The hexmap Package

To keep ewing lightweight and independent of heavy interactive Leaflet dependencies (leaflet, leaflet.extras, nhdplusTools), all live USGS HUC subwatershed lookup, OpenStreetMap feature clipping, and interactive Leaflet mapping applications have been refactored into the standalone hexmap package.

Package Citation & Installation

Users wishing to interactively explore USGS subwatersheds on Leaflet maps or download custom HUC boundaries can install hexmap:

# install.packages("pak")
pak::pak("byandell/hexmap")

hexmap Interactive Application Features

  1. Leaflet Map Discovery: Interactive reverse-geocoding and landmark search (get_huc_from_point, get_hucs_from_polygon).
  2. Dynamic Feature Isolation: Polygon clipping (osmdata::getbb()) for restricting watersheds to island landmasses.
  3. Interactive Hex Mapping: hexmapApp() provides interactive Leaflet controls, slider extent scaling, and .rds spatial dataset downloads.

3. Offline Spatial Architecture & Multi-Landscape Cache Engine (get_site_cache_file)

ewing resolves pre-computed .rds spatial datasets ([site]_layer.rds, [site]_features.rds, [site]_landmarks.rds) using get_site_cache_file(filename, site):

  • Resolves dataset paths dynamically across installed package directories (extdata/[site]) and development source trees (inst/extdata/[site]).
  • Enables ewing spatial simulations to scale to additional landscapes (e.g. site = "yellowstone", site = "madeline_island") with zero network API dependency.