Getting started with GIS open data

Coordinate systems and EPSG

WGS84: EPSG:4326
TWD97 geographic coordinates: EPSG:3824
TWD97 TM2 121 (commonly used on Taiwan island): EPSG:3826
TWD97 TM2 119 (commonly used on western offshore islands): EPSG:3825
TWD67 TM2 121: EPSG:3828
Web Mercator: EPSG:3857

TWD97 and WGS84 are generally close for typical student projects, but verify the epoch, purpose and required accuracy. TWD67 requires an appropriate parameter or grid transformation; never simply relabel it TWD97.

Importing data into QGIS

SHP: drag the complete ZIP into QGIS. Keep the companion files; the .shp file alone is insufficient.
GeoJSON: add a vector layer in QGIS and check the declared source CRS.
KML/KMZ: add a vector layer in QGIS and inspect layers and attributes.
CSV: use Add Delimited Text Layer. Set X to longitude/easting and Y to latitude/northing, with the correct EPSG.
XML: inspect its structure first. Coordinates alone do not make it a directly readable spatial layer; convert to GeoJSON or coordinate CSV if needed.
WMTS: add the NLSC GetCapabilities URL to a QGIS WMS/WMTS connection. Select a layer and tile matrix and check its license.
WMS: create a QGIS WMS/WMTS connection using the provider’s service URL; verify layers and supported CRS.

NLSC WMTS GetCapabilities ↗

Python CRS conversion example

Verify the source CRS first: assigning a CRS and transforming coordinates are different operations. Convert back to WGS84 before exporting interoperable GeoJSON.

from pathlib import Path
import geopandas as gpd

# pip install geopandas pyproj
source = Path("data.shp")
if not source.is_file():
    raise FileNotFoundError(source)
data = gpd.read_file(source)
if data.crs is None:
    raise ValueError("Missing source CRS: check the provider metadata first")
projected = data.to_crs(epsg=3826)
# RFC 7946 GeoJSON uses WGS84 longitude / latitude, not projected metres.
projected.to_crs(epsg=4326).to_file("output.geojson", driver="GeoJSON")

Licensing and attribution

A directory does not give every dataset the same license. Check each source for licensing, attribution, update dates and restrictions. Unconfirmed licenses are shown as “See original website”.

Taiwan Open Government Data License, version 1.0 ↗

OSM · ODbL ↗ · Natural Earth · Public Domain ↗ · EDGAR · CC BY 4.0 ↗