What is the Rest-of-the-World (RoW) and how is it calculated?
Rest-of-the-World (RoW) is a geographical area. Datasets (activities) with this geography contain data for the rest of the world datasets which are not represented in the ecoinvent database. The activities with the Rest-of-the-World geographic location are generated automatically during the linking by the database service layer.
In the Undefined system model, i.e. before linking, all the regional as well as the global (GLO) activities are present (see example below).
The barley production is available in the undefined system model for four different geographies; France (FR), Germany (DE), Spain (ES) and global (GLO). The global activity represents an average of all barley production in the world. The production volume [kg of barley produced / year] is 1.03E+10 kg in France (PVFR), 4.63E+09 kg in Germany (PVDE), 1.16E+10 kg in Spain (PVES) and 1.39E+11 kg in the whole world (PVGLO).

One of the first steps of the linking is the generation of the RoW activity. In ecoinvent v3.2 (2015) and higher the RoW is generated as an exact copy of the GLO dataset with uncertainty adjusted.
The production volume (PV) of the RoW dataset is then calculated;
PVRoW = PVGLO - PVFR - PFDE - PVES = (1.39E+11) - (1.03E+10) - (4.63E+09) - (1.16E+10) = 1.12E+11 kg/year
PVRoW = PVGLO - PVFR - PFDE - PVES = (100%) - (7.4%) - (3.3%) - (8.3%) = 80.9%

The newly generated RoW is then linked with activities of an adequate geographies creating RoW specific supply chain.
If the regional activities are covering the production of the product in the whole world the global dataset will be exactly weighted (by production volumes) average of the regional datasets. In that case the RoW activity will not be generated during the linking.
The RoW activity is also not generated if its production volume (of either the reference product or by-products) is <0.5% of the production volume of the global dataset.
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What is an activity in ecoinvent version 3?
What are global background activities and where do they come from?
What is a market and how is it created?
In which situations are direct activity links used?
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Why is the amount of the reference product changing?
What is linking and what happens during the linking process? Attributional System Model
What is linking and what happens during the linking process? Consequential System Model
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What do the shortcuts, such as CH, RER, RoW and GLO mean?
The ecoinvent database in Environmental Product Declarations (EPDs)
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How to interpret the uncertainty fields in ecoinvent?
What are the LCIA methods ecoinvent is publishing the impact assessment results for?
APOS: why do I have carrots on my recycled aluminium?