What is the SIU and where does its data come from?
The Sistema de Información Urbana (SIU) is the public planning and land information system provided for in the first additional provision of Spain's consolidated Land and Urban Renewal Act (TRLSRU). The Ministerio de Vivienda y Agenda Urbana runs it with the regional governments. A working group of every region plus local authority representatives agreed a common minimum data model, and data-sharing agreements are in place with Aragón, Asturias, Cantabria, Castilla y León, Castilla-La Mancha, Extremadura, Galicia, Madrid, Murcia and the Basque Country.
The SIU now holds planning data for 5,898 municipalities, where 98.61% of the population lives. The national statistics office (INE) counts 8,132 municipalities, so many small villages are missing. The SIU viewer is free, needs no account and works on a phone.
The SIU translates each town's plan into one shared vocabulary so that places can be compared. That makes it a good first look, and it is also why it cannot replace the plan: it flattens categories that each region names its own way.
How do I find my plot and its land class?
The help manual linked from the Ministry's page describes three tools: the search box, the information layers and the information panel. The viewer itself is in Spanish.
- Find the area. The search box takes the name of a planning sector, a region, province, urban area or municipality, or a postal address. It does not take a cadastral reference, so zoom in to the plot with the cadastral plan beside you.
- Switch on the layer. Among the information layers, turn on "Clases de suelo" (land classes). The same group holds "Ámbitos o sectores" (planning sectors) and "Grado de desarrollo" (how far development has gone). Each layer shows its legend, and you can change its transparency.
- Click the plot. The panel shows the selected area in each active layer and, separately, figures for the whole municipality.
- Note the plan. For the municipality, the planning tab gives the type of plan in force, its approval date and a link to the regional planning register or viewer. You will need these when you write to the town hall.
- Check the data date. The land class, area and sector layers the Ministry publishes for download are dated 2 December 2025, and the tabular data 19 June 2026. A later change to the plan may not be there yet.
The viewer draws planning areas, not property boundaries. If a class boundary runs through the plot, ask the town hall for the rules on each part. To pin down the exact land, start from the cadastral reference.
What does each class in the legend mean?
The Ministry's methodology notes define the SIU classes as follows:
- Urbano consolidado (consolidated urban): land already part of the town, serviced or close enough to count as a building plot, sometimes with minor works alongside the house.
- Urbano no consolidado (unconsolidated urban): urban land that still needs servicing or facilities; owners may have to share costs and benefits.
- Urbanizable delimitado o sectorizado (defined developable): land the plan has marked out to join the town through a development process with a timetable.
- Urbanizable no delimitado o sectorizado (undefined developable): a reserve for future growth, with no conditions or timetable set.
- No urbanizable (non-developable): land kept out of development for protection, its natural or farming value, public property, hazards or other reasons.
- Sistemas generales no adscritos (unassigned general systems): not a class in the strict sense; the SIU shows them separately when the plan does not assign them to one.
"Developable" does not mean you can build now. Until development is finished, national law treats the land as rural (TRLSRU, art. 21), and the floor area a plan shows does not become part of your property just by appearing on a map (art. 11). If you are unsure what each class allows, see the guide on rustic, urban and developable land.
Why does the Catastro say something different?
Because the Catastro classifies land for tax. Under article 7 of the Cadastre Act, land counts as urban when the plan classes it as urban, but also when it is developable land in a sector with detailed planning, when it is part of a settlement's network of services, and in other cases. A council tax (IBI) bill can say "urbano" on land the plan does not yet let you build on, and the other way round.
Neither reading tells you what you can build. That comes from the plan in force, its amendments and the zoning rules for the area, explained in the guide on what you can build on a plot.
What if my municipality is missing or the plan is old?
If the search box cannot find the municipality, or the land class layer comes up empty, do not guess. Go to the town hall's planning department and, where there is one, the regional planning viewer, which the SIU links to when it knows it.
Look at the date of the plan too. Plenty of towns still run on a general plan from the 1990s, but it may have spot amendments, partial plans or a full review under way that the SIU has not picked up. Ask about all of these in writing.
What the viewer does not tell you
The SIU does not show whether a house has a licence, whether the plot is a serviced building plot, or how much floor area you may build. It does not settle boundaries, rights of way, charges on the Land Registry or unpaid development costs. You can switch on reference layers such as the Catastro, Natura 2000, watercourses with a surveyed public water boundary, the coastal public domain, flood zones, seismic risk and radon, but decide on each topic from its own source; for flooding, use the SNCZI flood viewer.
The town hall is the planning and licensing authority (Local Government Act 7/1985, art. 25.2.a), and you are entitled to written information on the planning rules for a specific property (TRLSRU, art. 5). Ask for that report, certificate or cédula urbanística with the cadastral reference, a plan and what you intend to do, and make the deposit contract (arras) conditional on the answer. A screenshot of the viewer does not bind the officer who will sign the licence.