ISO 3166-1 Alpha-3 Country Codes

What is ISO 3166-1 alpha-3?

ISO 3166-1 alpha-3 is the international standard for three-letter country codes published by the International Organization for Standardization (ISO). Each code uniquely identifies a country or territory (e.g. SLE for Sierra Leone, LAO for Laos).

Why WorldPop requires ISO3

WorldPop publishes population rasters organized per-country. Unlike some spatial data services, WorldPop files cannot be queried by bounding box -- you must specify the country by its ISO3 code to locate the correct raster. This is also confirmed by the DHIS2 climate/Earth-observation tools (dhis2eo).

The WorldPop URL pattern for GeoTIFF rasters is:

https://data.worldpop.org/GIS/AgeSex_structures/Global_2000_2020_1km_UNadj/
  constrained/{YEAR}/{ISO3_UPPER}/{iso3_lower}_{sex}_{age}_{year}.tif

• Uppercase in URL path segments: /SLE/
• Lowercase in filenames: sle_f_0_2020.tif

Common codes used in this project

Code	Country	Notes
SLE	Sierra Leone	Default for dev DHIS2
LAO	Laos	Previously used as default
VNM	Vietnam

Where to find ISO3 codes

• ISO 3166-1 alpha-3 -- Wikipedia
• ISO Online Browsing Platform

How ISO3 is used in the codebase

1. ImportQuery.iso3 -- The iso3 field on ImportQuery (packages/prefect-climate/prefect_climate/schemas.py) is the main entry point. It is passed through every task in the flow.

2. build_tiff_url() -- Constructs the download URL by inserting the ISO3 code in both uppercase (path) and lowercase (filename) positions.

3. Default value -- When no ImportQuery is provided the flow defaults to iso3="SLE" (Sierra Leone), matching the dev/play DHIS2 instance.