Core concepts — Economics.

The platform has a small set of core ideas. Understanding them is most of the model. This page walks through them with two concrete examples — tap water in Antwerp, and a loaf of bread in Ghent. No LCA background assumed.

The vocabulary

Activity

An activity is a process. "Bake bread in a Belgian bakery, 2026." "Pump tap water in Antwerp." "Generate electricity, French grid mix."

An activity is a verb — the recipe. What goes in, what comes out. Every activity has a name, the organisation that contributed it, the quantity it's defined at (e.g. "1 kg of bread"), and optionally a geography and a reference year.

Multiple activities can serve the same purpose. There can be a Belgian bread activity, an Italian one, a Vermont artisan one. They all produce "bread" but with different inputs, geographies, and sources — and different accuracy.

Flow

A flow is one edge leaving or entering an activity. There are two kinds, distinguished by what the flow points at:

Product (intermediate) flow — an activity's output that becomes another activity's input. "The bread activity consumes 0.7 kg of wheat flour" is an input flow on the bread activity. It is wired to the producing activity's output flow, which is what makes the graph an actual graph.
Elementary flow — a resource crossing between the activity and a physical compartment of the Earth. "The bread activity emits 0.05 kg of CO₂ to the troposphere" is an output flow pointing at a natural sphere.

Every flow declares a resource (the what), a value, a unit, and a direction (input or output).

Spheres

Spheres are the physical compartments elementary flows target — a small hierarchy:

Geosphere      → Deep Subsurface · Subsurface · Soil
Hydrosphere    → Freshwater · Brackish Water · Ocean
Atmosphere     → Troposphere · Upper Troposphere · Stratosphere
Technosphere   ← holds product / intermediate flows

The three natural roots (plus their sub-spheres) are where flows leave or enter nature. The Technosphere is where product flows live — so a chain's only two terminals are a natural sphere or another activity.

Resources, units, geographies

Resources are the what of a flow — CO₂, electricity, wheat flour. Each has a type: substance, mineral, energy, phenomenon, land, biological, socioeconomic, product, or financial. (financial is money-as-a-resource, denominated in currency units.)
Units carry a symbol (kg, kWh, l), a dimension, and where possible an SI factor.
Geographies carry an identifier, a name, a type (global, country, region…), and a parent — so Belgium sits inside Europe sits inside global.

Accuracy

Every flow carries an accuracy made of three components: source (how credible is the originating dataset), geography (how well the flow's geography matches the activity consuming it), and temporal (how current the data is). The accuracy propagates up the chain, and every result carries a grade from A to F. See Accuracy & confidence.

The big picture

Sphere ←── elementary flow ── Activity ── product flow ──→ (Technosphere)
                                 │                              │
                                 │                              └──→ producing activity's output flow
                                 ├── has many input flows
                                 └── has many output flows

A bread activity has roughly seven flows: three input product flows (flour, water, electricity), one output product flow (the bread), and three elementary output flows (CO₂, CH₄, NOx to the troposphere).

Worked example: tap water in Antwerp

A simple activity, as it is described.

name:           Tap water supply, Antwerp
geography:      Belgium
unit:           litre        (defined at 1 l)
source:         ecoinvent 3.10
reference year: 2023

Water is extracted from rivers and groundwater, treated, pumped through pipes, and delivered to taps. Two of its flows matter most:

Input — electricity for pumping (a product flow). To supply 1 litre of tap water, the process consumes 0.0004 kWh of Belgian electricity. The flow declares the resource and value; a link connects it to the specific Belgian-grid activity that produces that electricity.

Output — CO₂ to atmosphere (an elementary flow). Supplying 1 litre emits 0.000636 kg of CO₂ to the Troposphere sphere.

Is this a leaf? A leaf activity is one whose chain ends at nature — an emergent property discovered by walking the graph, not a declared flag. Tap water's electricity input is linked to the Belgian grid activity, so it is not a leaf: the deep upstream — coal mine → transport → power plant → grid → tap water — is all connected.

Worked example: bread in Ghent

A more complex case, with geographic substitution.

name:           Bread baking, Belgian bakery
geography:      Belgium
unit:           kg
source:         user-contributed, reviewed
reference year: 2025

Its input flows, each wired to the activity that produces it:

Input (resource)	Supplier activity	value	unit
Wheat flour	Flour milling, European average	0.7	kg
Tap water	Tap water supply, Antwerp	0.4	l
Electricity	Belgian electricity grid	0.3	kWh
Yeast	Yeast production, global average	0.01	kg

Notice the substitutions: flour uses the European average (one geographic level up from Belgium); yeast uses a global average (no European yeast activity exists yet). These substitutions aren't errors — they are simply which producing activity is available, and each one lowers the geography component of the flow's accuracy. A weak match is shown, never hidden.

The bakery also has direct emissions — elementary output flows from the oven burning natural gas: CO₂, CH₄, and NOx to the Troposphere.

Put together, a consumer sees a single carbon number and a confidence grade; a prosumer sees the top contributors and where each was substituted; a professional sees the full per-flow, per-component accuracy breakdown. Same stored graph, three readings.

What you can do with the graph today

Today the platform stores the activity graph and reads it back over a public API: full-text search and browse over activities, resources, units, geographies, and impact data; list an activity's flows; and walk one level up its supply chain. The full multi-level traversal, impact totals, and accuracy grades described above are the model's direction of travel — the schema is shaped to deliver them.