## 3 - 10 = 65529. What?

Yes, the formula above is correct. Well, it depends on what we mean by correct. NDVI does not make sense Imagine the following situation. We have fetched a cloud-free mosaic of Sentinel 2 satellite data and want to measure NDVI (Normalised difference vegetation index), which uses red and near-infrared bands within this simple formula. NDVI = (NIR - Red) / (NIR + Red) The results are normalised, which in this case means that they lie between -1 and 1....

January 16, 2021 · 2 min

## The journey of an algorithm from QGIS to GeoPandas

This is a short story of one open-source algorithm and its journey from QGIS to mapclassify, to be used within GeoPandas. I am writing it to illustrate the flow within the open-source community because even though this happens all the time, we normally don’t talk about it. And we should. The story Sometimes last year, I asked myself a question. How hard would it be to port topological colouring tool from QGIS to be used with GeoPandas?...

June 21, 2020 · 4 min

## Morphological tessellation

Imagine you are trying to analyse a city, and you want primarily to understand its structure. You look at buildings, their dimensions and patterns they form, you look at a street network, and then you want to understand detailed patterns of density. This last point requires a specification of an aerial unit, and morphological tessellation is one of the most detailed options. I don’t want to talk only about density, but let’s use it as an illustration....

May 30, 2020 · 4 min

## Line simplification algorithms

Sometimes our lines and polygons are way too complicated for the purpose. Let’s say that we have a beautiful shape of Europe, and we want to make an interactive online map using that shape. Soon we’ll figure out that the polygon has too many points, it takes ages to load, it consumes a lot of memory and, in the end, we don’t even see the full detail. To make things easier, we decide to simplify my polygon....

April 27, 2020 · 5 min

## Confused terminology in urban morphology

This is a short introduction of our recently published paper Measuring urban form: Overcoming terminological inconsistencies for a quantitative and comprehensive morphologic analysis of cities, which is essentially one of the background chapters of my PhD (hopefully finished later this year). When I started my work, which is focusing on measuring of urban form (or urban morphometrics) - see momepy - one of the first things I wanted to do was to understand what people were people measuring so far — the natural thing to do....

March 4, 2020 · 4 min