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GDAL, the Geospatial Data Abstraction Library, was designed to interact with raster and vector (geospatial) data. Over time it has evolved to include sophisticated data manipulation and analysis tools. The GDAL source code is C++, which makes it fast to run but difficult to install. Many software and applications use GDAL for handling and analyzing…
A shapefile is a file format that represents geographic data in vector format. Shapefiles define points, lines, and polygons. The shapefile format was developed by ESRI and is frequently referred to as an ESRI shapefile. Shapefiles are not the only way to represent vector data. Geopackages, GeoJSON, KML, CSV, and database structures also represent vector…
Web maps are the best way to share data with an audience. They are also some of the most tedious and difficult map products to make. Web maps give the creator control over which aspects of the data to share, how to display the data, and who to share the data with. They also make…
Have you ever seen those really awesome visualizations of rivers that are made with elevation data? You know, the ones where you can see the channels meander through the floodplain? Those visualizations are made using relative elevation models (REMS), which are also known as detrended DEMs. Visualizing data for rivers in GIS and map visualizations…
With QGIS reprojections can be calculated with the export data tool, the reproject layer tool, and GDAL Warp. Reprojecting layers (i.e., converting them to a different coordinate reference system, or CRS) is often an important step of geospatial analysis to ensure layers are properly registered and perform distance and area calculations. I’ll demonstrate how to use the export, reproject, and warp methods to reproject raster and vector layers.
In cartography and GIS, it is to display two different products side by side to make comparisons. This is a powerful and often necessary feature of any serious GIS software. QGIS makes it possible to display multiple map views side by side. However, there are a few steps that are not well documented that you’ll…
In geographic information science (GIS), remote sensing is the act of acquiring information about the features of the Earth’s surface from a distance. Remotely sensed data are acquired from many different platforms including, satellites, aircraft, and fixed instruments with many different sensors including, spectral imagery (cameras), lidar, and radar. The most common form of remotely…
Image classification techniques are at the heart of modern remote sensing. Image classification is a method of extracting usable information from images. Without classification, images are just a collection of numbers that represent colors and it’s very difficult to obtain any quantifiable information about a landscape from data like that. With remote sensing techniques, we…
If you’re looking for a way to automate your GIS workflows and products, the QGIS Python API (PyQGIS) may be able to save you a lot of time. With PyQGIS you can write Python code that automates QGIS tasks that range from loading data to creating and saving map layouts. I’ve used PyQGIS to write…
GIS software makes it possible to create maps that contain a lot of powerful and important information. However, sharing those maps and information with non-GIS users can be difficult, especially when maps contain multiple layers. Others may not have GIS software or know how to use it, and an image of a map may not…
Image classification is the process of using numerical methods to automate the identification of objects in images and is a common method to interpret satellite imagery. With vast amounts of satellite imagery being collected every day it is next to impossible to manually classify satellite images for their many purposes. Instead we rely on numerical…
When working with spatial data it is common to have a file that has columns containing coordinates and attributes. Often points are represented in Excel or CSV (comma-separated values) files. To work with these data with geospatial software (like QGIS or ArcGIS) they need to be converted to a geospatial file format, like a geopackage…
Contour lines are most often used to represent topography on two-dimensional maps and figures. However, they can represent spatially changing values for any variable. Creating, styling, and labeling contour lines can be a little tedious, and it takes a little bit of time to learn exactly which tools to use to do this in QGIS….
QGIS only has one basemap that is included by default, Open Street Map. However, QGIS does have the functionality to support many different types of basemap sources and services. Basemaps can be added to QGIS by copying the URL to a web map service and pasting the URL to the proper data source in QGIS….
This tutorial demonstrates how to install QGIS, set up and locate functions and tools in the QGIS interface, add spatial and tabular data to QGIS, perform simple GIS analysis, and create a formal map.
QGIS is a very powerful and customizable software. However, one of its shortcomings is that it only comes with one default basemap, Open Street Map. The great thing is that it is very easy to add other basemap sources to QGIS. Google Maps and Google Satellite are probably the most recognized map layers in the…
QGIS is an amazingly powerful, free GIS software. In my opinion, it’s the best free GIS software there is and even outperforms expensive, enterprise software in some instances (looking at you ESRI). QGIS is available for Windows, Mac, and Linux operating systems. There are two different options for installing QGIS and the installation process can…
The only basemap available with QGIS is Open Street Map. Open Street Map is a good, basic basemap but sometimes context from aerial imagery is required to properly convey the meaning of a map. The good news is that QGIS has a lot of options for adding in outside map sources. One great basemap for…
Many types of geographical data represent 3-dimensional features. Displaying these data in compelling visualizations can often be difficult when limited to a 2-dimensional screen or piece of paper. Luckily, QGIS has built-in support for visualizing 3D data so that you can show off your data with some exquisite visualizations. Creating 3D maps and visualizations in…
A spatial join is operation performed on spatial vector data that links the attributes of one feature set to the attributes of the closest feature in a second set. The result of a spatial join is a new feature set (vector layer) that contains the attributes of both the input feature and the closest feature…
For many GIS analyses, it is necessary to calculate the length, area, or perimeter of line or polygon features (i.e. geometries). These operations are referred to as calculating geometry. The QGIS tool that calculates feature geometries is the Field Calculator tool. There are some nuances and potential pitfalls when calculating geometry in QGIS. This guide…
Attribute tables display information about geographic features and are an essential element of any GIS. It is often necessary to subset, select, or remove features based on attribute data. Learning quick ways to accomplish these tasks can really speed up your GIS efficiency. One common, and very helpful, attribute table view is to show only…
Clipping raster layers is a basic operation in many GIS workflows. Since rasters often cover large spatial extents, it is often beneficial to extract (or clip) only the portion of the raster that pertains to a specific study area. This can greatly improve data load and rendering times and decrease the time needed for tools…
With GIS analysis it’s a common occurrence that multiple raster tiles are required to cover a study area. For many analyses, and specifically hydrological analyses, a seamless, single raster is needed. The solution for combining multiple raster layers is to perform a raster merge, also referred to as a raster mosaic. QGIS uses the the…
Have you ever run into the problem where default symbology options aren’t enough and you need to create a custom color ramp? If so, you are not alone. I’m pretty picky about my visuals. Everything has to be just right. A big part of that is making sure color ramps are fit for both purpose…
False-color satellite images can be very useful to visually analyze different landscape characteristics. They also look really cool and are used to make very artistic maps and displays. False-color satellite images are created by displaying different band combinations with different colors. For example, a color near-infrared image is created by displaying data from the near-infrared…
Vegetation indices are a staple remote sensing product and the normalized difference vegetation index (NDVI) may be the most widely used vegetation index. To calculate NDVI you simply need appropriate imagery and a program that allows you to interact with the image data. QGIS is a great, free option for a GIS program that provides…
QGIS is great for analyzing spatial data but it’s often easier to export layer attributes for additional analysis in a program like Excel or R. To do that you need to export the data from a layer’s attribute table to a format that is readable by other programs. To export a QGIS attribute table as…