ArcGIS: Digitising From Aerial Imagery

Digitising Building Footprints Layer

I am updating the building foot prints layer manually by tracing from the most recent aerial imagery tileset available. Personally I don't see much point digitising the entire local government area but this is the sort of mundane tasks we get assigned now and then. It's not hard, just tedious and boring.

Orc Peon: Work work work!

- Warcraft 3

The reason I think this is pointless is because buildings slowly shift from their locations every year due to tectonic plate movement. This geological movement over time means that the building footprints layer needs to be constantly updated (maybe every 5 or 10 years).

Of course we could fix some of this by datum transformation, but I'm probably not going the one to do this, and by that time, other GIS officers be in my role, doing the same mundane tasks updating the layer by hand, and making incremental edits along the way. A full datum transformation would mean moving the entire dataset, creating even more errors. So i don't think the layer would be updated this way.

Buildings will also get erected or demolished over time. So you end up with a lot of errors if the layer is not updated regularly. We are building whole new residential subdivisions at the moment due to our record high population growth and urban development. Some parts of our jurisdiction where the aerial imagery has not been updated, the development is happening fast so we might see a vacant block of land on the aerial imagery, but it actually is fully developed residential estates (like Pitt Town and North Richmond). Due to budget cuts our aerial imagery will always be outdated as the organisation is not getting new tile sets annually.

If we were actually going to do something with the dataset (like strategic planning, urban design, flood engineering) then I can understand having a detailed data set for an important area of study or geographic extent. But doing this for all 2700 Square Kilometres is... well a waste of effort!

Note to self: In future don't make my team do something so pointless!



Amusing Insight From Aerial Imagery

Every now and then you see something interesting on aerial photography that wouldn't be evident from being on the ground. This could include unusual geological formations, patterns of urban development or a geoglyph of a penis, that can be seen from space.

Upon inspection of our jurisdiction, I came up with these two below:

Image

Someone has a giant pentagonal dodecahedron in their backyard? It's too big for a soccer ball. That thing is as large as the utility van nearby.



Image

When you use more water for your residential lawn than the plant nursery (probably on drip irrigation). Look how lush and healthy that lawn is compared to the wild grass in the surrounding blocks!




2018, journal