One of the fundamental aspects that you must take into account when buying a home or building your own under the self-promotion modality is the type of land on which it is built , since you will not have the same possibilities if it is a plot on urban land than on rustic or rural land. To clarify your doubts in this regard, at Hipotecas.com we explain the concept of the different types of land and in which cases you can build on rustic land.
Urban land typology
In Spain, there are, in general terms, two types of land at the urban planning level, according to Royal Legislative Decree 7/2015, of October 30 , which approves the consolidated text of the Land and Urban Rehabilitation Law : 
- Urban land: According to the aforementioned regulations, it includes land that, " being legally integrated into an urban grid made up of a network of roads, facilities and plots of land specific to the population centre or settlement of which it forms part, meets any of the following conditions:
- Having been urbanized in execution of the corresponding planning instrument.
- Having installed and operational, in accordance with the provisions of the applicable urban planning legislation, the necessary infrastructures and services , through their network connection, to satisfy the demand for the uses and buildings that exist or are foreseen by urban planning or to be able to have them without any other works than those of connection with the pre-existing facilities.
- Be occupied by the building , in the percentage of spaces suitable for it determined by the territorial or urban planning legislation, according to the planning proposed by the corresponding planning instrument.
- Land included in traditional rural centres legally established in rural areas is also considered to be urbanised land, provided that the land planning and urban legislation grants them the status of urban or similar land and when, in accordance with this, they have the facilities, infrastructure and services required for this purpose.
- Rural land: This covers all the cases not included in the previous section, with the rule also establishing that it is land " preserved by territorial and urban planning from its transformation through urbanisation , which must include, as a minimum, land excluded from such transformation by legislation on the protection or policing of the public domain, nature or cultural heritage, which must be subject to such protection in accordance with territorial and urban planning due to their concurrent values, including ecological, agricultural, livestock, forestry and landscape values, as well as those with natural or technological risks, including those of flooding or other serious accidents, and any others provided for by territorial or urban planning legislation."
This last assumption is the one that concerns us, that is, when the home is located on the previously called rustic land .
Can I build on rustic land?
By its very definition, it is not permitted to build on rustic or rural land . 
However, we must point out that it is the autonomous communities that have the authority to classify land and include some exceptions that may be of great interest to you if you are or plan to be the owner of a plot of this type.
For example, in Galicia, a new regulation was approved in February 2016 that allows buildings to be built on rural land as long as they are for agricultural or livestock purposes or tourist constructions, such as camps, sports or leisure facilities and rural accommodation. On the other hand, Law 5/2014 that regulates land in the Valencian Community introduces other exceptions for building on rustic land : that the property has more than one hectare, that no more than 2% of the surface is used for the building and that it is single-family, that it does not affect the topography of the land and that it has a water and sanitation network. 
For their part, the town councils are responsible for the development of the urban planning of their municipality, so you may find slight differences depending on the area in which the plot is located. And how can you find out what type of soil the property or plot is on? The best thing to do is to go to the corresponding town council and request an urban planning report from it.
In any case, it is advisable to be well informed about the possibilities available in your area for building on rustic land, otherwise you expose yourself to significant fines, the obligation to demolish the construction, and even a prison sentence.