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Introduction

This dataset contains 11,842,186 computer generated building footprints in all Canadian provinces and territories. This data is freely available for download and use.

License

This data is licensed by Microsoft under the Open Data Commons Open Database License (ODbL)

FAQ

What the data include:

11,842,186 building footprint polygon geometries from all Canadian provinces and territories in GeoJSON format.

What is the GeoJson format?

GeoJSON is a format for encoding a variety of geographic data structures. For Intensive Documentation and Tutorials, Refer to GeoJson Blog

Creation Details:

The building extraction is done in two stages:

  1. Semantic Segmentation – Recognizing building pixels on the aerial image using DNNs
  2. Polygonization – Converting building pixel blobs into polygons

Semantic Segmentation

DNN architecture

The network foundation is ResNet34 which can be found here. In order to produce pixel prediction output, we have appended RefineNet upsampling layers described in this paper. The model is fully-convolutional, meaning that the model can be applied on an image of any size (constrained by GPU memory, 4096x4096 in our case).

Training details

The training set consists of 3 million labeled images. Majority of the satellite images cover diverse residential areas in Canada. For the sake of good set representation, we have enriched the set with samples from various areas covering mountains, glaciers, forests, beaches, coasts, etc. Images in the set are of 256x256 pixel size with 1 ft/pixel resolution. The training is done with CNTK toolkit using 32 GPUs.

Polygonization

Method description

We developed a method that approximates the prediction pixels into polygons making decisions based on the whole prediction feature space. This is very different from standard approaches, e.g. Douglas-Peucker algorithm, which are greedy in nature. The method tries to impose some of a priori building properties, which is, at the moment, manually defined and automatically tuned.

Metrics

Building matching metrics on our evaluation set:

MetricValue
Precision98.7%
Recall72.3%

False positive ratio across the board is less than 0.5%.

We track various metrics to measure the quality of the output:

  1. Intersection over Union – This is the standard metric measuring the overlap quality against the labels
  2. Shape distance – With this metric we measure the polygon outline similarity
  3. Dominant angle rotation error – This measures the polygon rotation deviation

On our evaluation set contains ~45k building. The metrics on the set are:

Data Vintage

The vintage of the footprints depends on the vintage of the underlying imagery. Because Bing Imagery is a composite of multiple sources it is difficult to know the exact dates for individual pieces of data.

How good are the data?

Our metrics show that in the vast majority of cases the quality is at least as good as data hand digitized buildings in OpenStreetMap. It is not perfect, and false positives exist, but most areas look awesome.

What is the coordinate reference system?

EPSG: 4326

Will there be more data coming for other geographies?

Maybe. This is a work in progress.

Why is the data being released?

Microsoft has a continued interest in supporting the open data ecosystem.

Should we import the data into OpenStreetMap?

Maybe. Never overwrite the hard work of other contributors or blindly import data into OSM without first checking the local quality. While our metrics show that this data meets or exceeds the quality of hand drawn building footprints, the data does vary in quality from place to place, between rural and urban, mountains and plains, and so on. Inspect quality locally and discuss an import plan with the community. Always follow the OSM import community guidelines.

Province/TerritoryNumber of BuildingsUnzipped MB
Alberta1,777,439389
British Columbia1,359,628301
Manitoba632,982135
New Brunswick350,98971
Newfoundland and Labrador255,56851
Northwest Territories13,1613
Nova Scotia402,35881
Nunavut2,8751
Ontario3,781,847808
Prince Edward Island76,59016
Quebec2,495,801512
Saskatchewan681,553146
Yukon11,3953
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Contributing

This project welcomes contributions and suggestions. Most contributions require you to agree to a Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us the rights to use your contribution. For details, visit https://cla.microsoft.com.

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This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact opencode@microsoft.com with any additional questions or comments.

Legal Notices

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