Accuracy and reliability

Overall accuracy

No quantitative assessment of the accuracy has been made. The statistics are based on all relevant map sources for the land cover of Denmark. The quality is thus inherited from the sources: the Danish topographical maps, the field map, the habitat mapping by the municipalities etc.

At the level of detail used for publication, accuracy is assumed to be high. As for many other statistics, the higher level of detail, the higher the uncertainties.

Sampling error

Not relevant for these statistics.

Non-sampling error

Land cover: Measurement error in the land cover account stems from the original map sources. The methods used to consolidate the source maps reveal some measurement errors - and, to some extent, corrects them. The significance of measurement errors for the final accounts is assessed to be minimal. The most significant errors are associated with the comparison between 2011/2016/2018 and 2021. Is is difficult to do such comparison without measuring many 'changes' that are not real, but caused by improved mapping techniques etc. The method applied accounts for this by 'filtering out' some apparent changes, with the risk of underestimating changes from 2011 to 2021. Details on the method are available in the technical report, published by DCE.

Land use: There is an error source in the distribution of land in cases where one parcel has more than one use. The distribution is done using a simple model, which will not always reflect actual distribution of land use on the parcel.

Quality management

Statistics Denmark follows the recommendations on organisation and management of quality given in the Code of Practice for European Statistics (CoP) and the implementation guidelines given in the Quality Assurance Framework of the European Statistical System (QAF). A Working Group on Quality and a central quality assurance function have been established to continuously carry through control of products and processes.

Quality assurance

Statistics Denmark follows the principles in the Code of Practice for European Statistics (CoP) and uses the Quality Assurance Framework of the European Statistical System (QAF) for the implementation of the principles. This involves continuous decentralized and central control of products and processes based on documentation following international standards. The central quality assurance function reports to the Working Group on Quality. Reports include suggestions for improvement that are assessed, decided and subsequently implemented.

Quality assessment

The statistics are well documented and transparent, building on all relevant map sources for the land cover of Denmark. The quality is thus inherited from the sources: the Danish topographical maps, the field map, the habitat mapping by the municipalities etc. At the level of detail used for publication, accuracy is assumed to be high. As for many other statistics, the higher level of detail, the higher the uncertainties. An important strength of the land cover account is that it is a consolidated map, meaning that each area (10 x 10 metre cell) is assigned to just one land cover type. An expert assessment have defined the priorities used when the source maps are conflicting. The methods and assumptions made are documented in the technical report from DCE, as it is researchers from DCE that have delivered the expert assessments as well as the technical implementation.

The method is well documented, but it is also a newly developed method and there are few ways to assess the quality through comparisons (to earlier data or to other countries, as few countries have similar accounts yet). The data sources have very good coverage, but sometimes the data sources are conflicting and expert judgements have been made to prioritize between them. There is also an uncertainty stemming from the geo data not always having same reference.

Data revision - policy

Statistics Denmark revises published figures in accordance with the Revision Policy for Statistics Denmark. The common procedures and principles of the Revision Policy are for some statistics supplemented by a specific revision practice.

Data revision practice

Land use accounts have only been published once, so there have been no revisions. It has not been decided if there will be revisions along with (eventual) future publications.

Land cover accounts have been published four times - with the second, third and fourth publication the full time series have every time been revised to ensure comparability.