Cartographic bases are the foundation of a thematic map that is fit for purpose and truly useful to the viewer. Therefore, ensuring that its content is properly adjusted to the reality of each moment is key, just as important as updating the thematic information itself. This requires ongoing work that should be streamlined as much as possible. From Geograma, we propose a methodology to achieve this. Here we describe it for you.
The goal: to facilitate and speed up the updating of base maps.
Most thematic maps use cartographic information as a background. Although a large amount of public cartography exists today, depending on the subject matter, scale and purpose of the map, the cartographic bases to be included in the plans must be adapted to each type of map.
This makes it necessary to retouch existing information to generate customised information, prioritising certain elements and selecting what needs to be represented in order to highlight the main thematic information. These adapted bases for different plans often take many hours of editing.
Although specific information is the focus of the thematic maps and should be the main effort, the constantly changing environment means that the information in the base also needs to be updated, which presents a problem.
For its updating and maintenance, a methodology of change control of the information can be proposed to deal exclusively with these changes, involving less effort and allowing a control of the state of the cartographic base.
Process for updating a cartographic base for thematic mapping
One way of doing this update is by comparing different versions of information from official sources with regular updates. The 4-step methodology would be as follows:
1.- Detect the important elements to update in our base.
For example, depending on the scale of representation, it could be buildings and street axes. In other cases, updating the surrounding roads may be sufficient.
2.- Detect official sources
Among all the resources available for updating a cartographic base, there are public bodies that periodically update the information of interest to us. For example:
- National Geographic Institute (IGN): periodically updates the Transport Network.
- Cadastre: publishes its updated information every 6 months.
- Municipalities: updating of street maps, cartography, etc. depending on each entity.
- Autonomous Communities: updating of their cartographic bases.
3.- Compare the different versions
Once the sources useful for our base have been detected, we should check the latest version published with our base and save that version.
When the competent body of that information publishes an update, the previous saved version is compared with the current information. For this purpose, different ETL tools, GIS, etc. can be used.
By obtaining the changes between the two versions, we can update only the detected information, saving a lot of editing time.
4.- Update the area
If it is necessary to update the area around the detected elements that have changed (e.g. if a building changes, the environment may have changed), the most recent orthophoto can be used. The PNOA (National Aerial Orthophotography Plan) renews every 2 or 3 years the orthophotographs, with an accuracy sufficient for a 5.000
With this methodology, we are able to have our own cartographic base updated and controlled without having to revise it completely from time to time. In this way, we can invest the time gained in other actions that add value, ensuring that we always offer up-to-date and practical content.
If you think that this process would be perfectly adapted to the cartography of your project or organisation, Geograma encourages you to contact us to discuss it in more detail. Write to us!