Coordinate systems and GeoJSON

Geographic coordinates are interpreted as WGS 84 longitude/latitude (EPSG:4326). UTM zones use WGS 84 projected CRSs: EPSG:326xx for northern zones and EPSG:327xx for southern zones. Confirm the correct zone and hemisphere for the study area.

GeoJSON polygon area and perimeter are calculated using Turf.js geodesic functions. Input geometry must use longitude/latitude coordinates; projected coordinates are not automatically reprojected by the file calculator. Validate topology and coordinate order in a GIS before relying on the output.

EPSG:32629 — WGS 84 / UTM zone 29N · Turf.js area documentation · Turf.js length documentation

Spectral indices

NDVI = (NIR − Red)/(NIR + Red). The classic early application is Rouse et al. (1974), Monitoring vegetation systems in the Great Plains with ERTS, NASA technical report. NASA NTRS record.

McFeeters (1996), “The use of the Normalized Difference Water Index (NDWI) in the delineation of open water features,” International Journal of Remote Sensing, 17(7), 1425–1432. DOI: 10.1080/01431169608948714. This Green–NIR NDWI is distinct from other indices also abbreviated NDWI.

Zha, Gao & Ni (2003), “Use of normalized difference built-up index in automatically mapping urban areas from TM imagery,” International Journal of Remote Sensing, 24(3), 583–594. DOI: 10.1080/01431160304987.

Common Sentinel-2 band pairings: NDVI B8/B4; McFeeters NDWI B3/B8; NDBI B11/B8. Verify the sensor, processing level, resampling, and scaling before calculating. These formula citations do not validate a particular image product or classification.

Watershed morphometry

• Drainage density: Dd = total mapped channel length / basin area, with channel length in km and area in km².
• Form factor: Ff = A/Lb².
• Circularity ratio: Rc = 4πA/P².
• Elongation ratio: Re = 2√(A/π)/Lb.

These are standard descriptive geometric indices. Their interpretation depends on delineation scale, stream extraction threshold, map projection, and consistent definitions of basin length and perimeter. No universal flood design values are produced by these formulas.

Verification status

Publisher, DOI, NASA, EPSG, and Turf documentation links above were checked during preparation. The page intentionally does not claim that every regional paper previously listed in the source files has been verified. Do not add a regional application to the bibliography until its title, authors, year, journal and DOI have been checked against a publisher or indexing record.