Example – add population data in R:
GADM (Database of Global Administrative Areas) is the gold standard for boundary data. Version 3.6, released in late 2020 (with minor updates into 2021), remains one of the most widely used versions due to its stability, licensing clarity, and compatibility with legacy systems. However, novice users often struggle with file formats, projection mismatches, and API changes. download gadm data version 36 work
# Manual download method download.file("https://biogeo.ucdavis.edu/data/gadm3.6/Rsp/gadm36_USA_1_sp.rds", "gadm36_USA_1_sp.rds") usa_adm1 <- readRDS("gadm36_USA_1_sp.rds") Solution: Cross-reference with GADM 3.6’s lookup table. Download the gadm36_levels.gpkg and query the gadm36 table using SQL: Example – add population data in R: GADM
SELECT NAME_0, NAME_1, HASC_1, ISO FROM gadm36 WHERE ISO LIKE 'US%'; Here is how to work with the data after a successful download. Workflow A: Extract a single country from global Geopackage (fastest) If you downloaded the global Geopackage, you don’t need to re-download per country: # Manual download method download