1. Why do some buildings have their actual shapes while others are represented only by dots?

The shapes of the buildings come from OpenStreetMap, a collaborative mapping service, a kind of Wikipedia for maps. The data in OpenStreetMap is submitted by volunteers, so the image remains incomplete, covering mostly central cities and districts. However, OpenStreetMap is constantly updated; Our map will therefore be updated.

The City of Montreal should also release data later this year that will allow us to map all buildings.

2. Why are so many buildings gray?

The years the buildings were built were provided to us by the city's property valuation office, which had incomplete data. Missing addresses may include abandoned buildings, vacant lots, or undeveloped areas such as green spaces or parking lots. In some cases the year of manufacture is simply not available. Data on institutional buildings such as schools and churches were also incomplete in many cases.

According to the city's property investigation office, there is also no data available for properties on which several buildings have been built over the years.

It is also possible that when this map was created, the year of construction indicated for some points was not assigned to the corresponding building. Some points can represent multiple addresses. a single point then corresponds to a building in the group.

In total, 32,000 of the 350,000 buildings in the map (approx. 9%) do not have a construction date.

3. Are the construction dates correct?

Not all. The older the building, the greater the risk of errors in the data. In the land register, for example, the construction of the house at 17013, Boulevard Gouin Ouest, is dated to the year 1700 a cultural heritage documentThe same house was built in 1830.

Another example : these condos at 1451 Rue Notre-Dame Ouest were probably not built in 1600, i.e. before the city was founded. The Property Valuation Office explains that when an element of an old structure is present in a new building, such as a wall or foundation, the original year is often retained.

However, we have checked each of the iconic buildings we selected for presentation with the two experts to ensure that the founding dates are correct.

4. Why are the years divided unevenly in the legend?

We chose the colors based on the number of buildings built in a specific time period. Since most buildings were built after 1900, it made more sense to divide the later years into multiple colors to better understand the nuances.

5. How was this map designed?

The map has multiple data sources:

All data sources were brought together in order to assign a year to each of the different building types, if possible. The rest is made up of dots that represent addresses.

The data was prepared using the programming languages ​​Python and QGIS and visualized using the online software Carto.