Understanding property boundaries - quality, accuracy and legal significance

When you look at a property boundary on a map, you can get a clear picture of where it is - but how accurate is it? This article explains how the quality of boundaries is determined, what different measurement methods mean and how you can assess the reliability of the information.

What does the quality of a property boundary mean?

For each property boundary, there is information on the measurement method and the positional uncertainty (how accurately the position is determined). The positional uncertainty is given as an average error, usually in millimeters, and is almost always calculated or estimated from the measurement methods used in the data capture.

In other words, it shows how close the map boundary is to the actual position on the ground. The better the measurement method, the less uncertainty.

Different measurement methods and their accuracy

Property boundaries can be measured in several different ways, and the method used affects how accurately the boundary is placed on the map.

Boundaries measured by geodetic methods, such as total station, GPS or DGNSS, generally have very high accuracy - often only a few centimeters. These boundaries are the most reliable.

If the boundary has instead been determined by photogrammetric methods, i.e. from aerial photographs, the accuracy is lower and the uncertainty can be a few meters.

In the case of digitization, the boundary has been drawn from older maps or orthophotos, often manually. This means that the accuracy varies more, often within several meters.

In some cases, the boundary is placed based on cartographic location, which means it is based on visual interpretation rather than precise measurement data. In these cases, the position is approximate and may differ significantly from reality.

There are also boundaries that are interpreted according to the Land Code (JB 1:5). These are based on legal interpretation rather than measurement and therefore lack information on accuracy. In addition, for some boundaries, the measurement method is unspecified, which means that there is no information on how they were derived or how accurate they are.

In addition, for each boundary, two dates are given - one showing when the boundary was created and one for the last modification. However, a change does not necessarily mean that the location information itself has been updated.

Historical development

Between 1935 and 1977, extensive field work was carried out to create a nationwide mapping system in Sweden. The geometric quality varies over time, and older maps in particular often lack a known coordinate system. The dimensions and angles of a property boundary may be given in relation to existing objects in the terrain, such as a house corner or a boundary cairn. In general, it can be said that property boundaries in more built-up areas are of better quality.

During the late 20th and early 21st centuries, much of the material was digitized and completed, which improved the quality. Nevertheless, there are still areas where boundaries are incomplete or simplified.

Examples of differences in accuracy

Black boundaries in the image example have been produced using both table and screen digitization with orthophoto as the basis and have an average error of 4.5 to 5.0 meters.

The green boundaries here have all been measured using geodetic methods, some using a total station and others using network RTK. The accuracy here is significantly better with only a few centimeters mean error.

Legal significance

Property boundaries on maps are indicative, not legally binding. The quality varies and the position is approximate.
According to Chapter 1, Section 3 of the Land Code, it is always the boundary mark in the ground that is legally valid. The legally valid documents are the cadastral survey map together with decisions and protocols, which are available at Lantmäteriet.

Summary - what does this mean for you as a user?

• The map's property boundaries show an approximate position, not the exact one.
• Use the information as a guide, not as evidence in legal matters.
• For legal demarcation, cadastral documents from Lantmäteriet are required.
• Metria reports the quality and measurement method so that you can assess how reliable the information is.

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