(Source: "Achieving land degradation neutrality at the global level," a publication produced by the Global Mechanism of the UNCCD)
Setting the LDN baseline and assessing land degradation trends require reliable data. The indicators should be computed primarily, and to the largest extent possible, using comparable and standardized national official data sources. Only in their absence or to complement such data should global data sources be used.
In the long term, all countries should ideally be able to perform relevant data collection, analysis and report on land degradation, independently.
A tiered approach is recommended for the computation of the indicators:
Tier 1 (default method): Global/regional earth observation, geospatial information and modelling
Tier 2: National statistics based on data acquired for administrative or natural reference units (e.g. watersheds) and national earth observation
Tier 3 (most detailed method): Field surveys, assessments and ground measurements
This approach enables national authorities to use methods consistent with their capabilities, resources and data availability and facilitates comparability at global level.