When trying to automate your GIS workflows, one important step is the production of maps. Creating and exporting maps in QGIS is done via the Print Layout. One can automate creation of maps via the a rich Python API using the QgsLayout class.
Continue readingReclassifying Rasters using gdal_calc
gdal_calc is one of the lesser used tools among the GDAL utilities. There aren’t many examples of using it in the wild and some advanced features are not well documented. I am finding myself using it a lot lately and have discovered some really powerful use cases.
Continue readingOptimizing Office Commute with Uber Movement Data
In a previous post, I showed how to use the Uber Movement Travel Times data to create isochrones. In this post, we will explore another use case of this dataset. Say you are concerned about loss of productivity due to long commute times of your employees and wonder if a change in office times might help them get to the office faster. A similar analysis can be done to see if a change in office location will result in better or worse commutes.
Here’s the hypothetical scenario “Given the location of an office and location of homes of employees, determine their current commute times for office timings of 9am-11am and 5pm-6pm. If the office timings were changed to non-peak timings of 7am-8am and 3pm-4pm, what would be the time savings?“
Continue readingGenerating Random Points with a Specific Distribution
Generating pseudo-random data is important for many aspects of research work. QGIS provides for many methods of generating random points to facilitate this.
Recently, I ran into a problem where I wanted to generate random points inside a polygon – but I wanted the random points to have a certain distribution. I wanted to generate a dataset showing employee home locations for a company. Given a city boundary and the location of office, I wanted to have a point layer that showed where the employees lived. A simple ‘Random points within Polygon’ algorithm would not work here, since the distribution of points would not be uniform within the city.
Continue readingConvert between Orthometric and Ellipsoidal Elevations using GDAL
When working with elevation data, sometimes you may discover that 2 datasets from different providers have very different elevation values for the same location. A common reason for this being each dataset being referenced to a different surface.
Continue readingFuzzy Table Joins in QGIS
Table Joins are a way to join 2 separate layers based on a common attribute value. QGIS has a Join Attributes By Field Value algorithm that allows you to table joins. A limitation of this algorithm is that the field values must match exactly. If the values differ slightly – the join will fail. There are many times where you are trying to join 2 layers from different sources and they contain values which are similar but may not match exactly. Fortunately QGIS now has built-in fuzzy string matching functions that can be used – along with Aggregate function – to do table join based on fuzzy matches.
Continue readingAnalyzing Urban Mobility with Uber Movement Data
Mapshaper is a free and open-source software for spatial data processing. It is written in javascript and runs in your browser without any extra plugins and can perform a range of analysis. It started out as a tool for topologically-aware simplification, but has evolved into a swiss army knife of spatial data processing tools. All processing is done in the browser locally, and I have found that it can handle large volumes of data easily and processing is usually much faster than desktop based GIS software.
Continue readingFind Neighbor Polygons using Summary Aggregate Function in QGIS
Read my previous posts Summary Aggregate and Spatial Filters and Advanced Aggregate Expressions to Automate QA to learn more about the powerful aggregate function.
Continue readingAdvanced Aggregate Expressions to Automate QA in QGIS
This post is the continuation of Summary Aggregate and Spatial Filters in QGIS. I have been exploring aggregate functions more and have found interesting ways to automate tasks in QGIS. One such example is helping automatically keeping track of feature edits to help with Quality Assurance (QA).
Continue readingSummary Aggregate and Spatial Filters in QGIS
QGIS expression engine has a powerful a summary aggregate function that can do spatial joins on the fly. This enables some very interesting uses.
Continue reading