Posted on December 28, 2022 (Updated on July 21, 2025)

Digitizing historical Brazilian map in QGIS3.4

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Unearthing Brazil’s Past: A Simple Guide to Digitizing Old Maps with QGIS

Ever wondered what Brazil looked like centuries ago? Historical maps are like time machines, offering incredible glimpses into the past. They reveal how landscapes and societies changed over time, showing everything from old colonial settlements to the territories of indigenous peoples, and even the early routes of farms and roads. The problem? These maps are often just old paper or scanned images, not easily usable in today’s digital world. That’s where digitizing comes in – it’s like giving these old maps a new lease on life!

In this guide, I’ll walk you through how to digitize historical Brazilian maps using QGIS 3.4. Don’t worry, it’s not as scary as it sounds! QGIS is a free, open-source software that’s surprisingly powerful. We’ll cover everything from prepping your map image to creating digital versions that you can actually use for research, analysis, and even cool visualizations.

First Things First: Getting Your Map Ready

Before you dive in, you’ll need a digital copy of your historical map. If you have the original, scanning it is the way to go. If not, check out online archives like the David Rumsey Map Collection or Old Maps Online – they’re treasure troves! Just make sure the image you get is clear enough to make out the details. A blurry map will only give you a headache later on.

Installing QGIS: Your Digital Swiss Army Knife

Next up, download QGIS from the official website. Think of it as your digital Swiss Army knife for all things map-related. Once it’s installed, you need to make sure the “Georeferencer GDAL” plugin is up and running. This little tool is what lets us “pin” the old map to the real world. To find it, go to Plugins > Manage and Install Plugins, search for “Georeferencer GDAL,” and tick the box to activate it. Easy peasy!

Georeferencing: Pinning the Past to the Present

Okay, this is where the magic happens. Georeferencing is the process of giving your map image real-world coordinates. It’s like telling QGIS, “This point on the map is actually here on Earth.” Here’s the breakdown:

  • Open the Georeferencer: Go to Raster > Georeferencer.
  • Load Your Map: Click “Open Raster” and select your historical map image.
  • Find Ground Control Points (GCPs): This is key. GCPs are points you can identify on both the old map and in the real world (or on a modern map). Think of things like landmarks, road intersections, or even the corners of old coordinate grids. The more GCPs you use, the more accurate your map will be. I usually aim for at least ten, spread out across the entire map.
  • Add Those GCPs: For each GCP, click on the exact spot on your historical map. A window will pop up, asking for coordinates. If you know them, great! If not, you can use the “From map canvas” option. This lets you find the same spot on a modern map loaded in QGIS. It’s super handy!
  • Tweak the Settings: Go to Settings > Transformation Settings. For “Transformation type,” I recommend “Thin Plate Spline” – it works well for most old maps. Then, pick a “Target CRS” that’s right for Brazil. SIRGAS 2000 / UTM zones are a good bet (like 24S or 25S, depending on where your map is). Give your georeferenced map a name and location, and make sure “Load in QGIS when done” is checked.
  • Let the Magic Happen: Click File > Start Georeferencing (or just hit the play button). QGIS will warp the image based on your GCPs, creating a new, georeferenced version of your map.

    • Digitizing: Tracing the Stories

    Now that your map is georeferenced, you can start tracing the features you’re interested in. This means creating digital shapes (points, lines, or polygons) that represent things like rivers, roads, or old property boundaries.

  • Create New Layers: Go to Layer > Create Layer > New GeoPackage Layer. A GeoPackage is like a container for all your digital map data. For each type of feature you want to trace, create a separate layer (e.g., one for rivers, one for roads). Choose the right “geometry type” (Point, LineString, or Polygon) and set the CRS to match your georeferenced map. You can also add fields to store information about each feature, like its name or type.
  • Start Editing: Select the layer you want to work on in the Layers panel and click the “Toggle Editing” button.
  • Trace Away!: Use the “Add Feature” tool to start tracing. Click on the map to add points (vertices) that define the shape of your feature. For polygons, trace the entire outline. For lines, click along the path. For points, just click on the location.
  • Add Information: After you create a feature, a window will pop up, asking for more information. Fill in the details for each field in the attribute table.
  • Make it Snappy: Enable snapping to make sure your lines and shapes connect perfectly. Go to Settings > Options > Digitizing and check “Enable snapping by default.” Set the “Default snap mode” to “Vertex.”
  • Save, Save, Save: Don’t forget to save your work regularly by clicking the “Save Edits” button!
  • Done for Now? Click the “Toggle Editing” button again to stop editing the layer.

    • Analyzing and Visualizing: Bringing the Past to Life

    Once you’ve digitized your map, the real fun begins! You can use QGIS to analyze the data, calculate distances and areas, and create maps that show off your findings. You can even export the data to other programs or share it with other researchers.

    Final Thoughts

    Digitizing historical Brazilian maps with QGIS 3.4 is a fantastic way to unlock the secrets of the past. It might seem a bit daunting at first, but with a little practice, you’ll be amazed at what you can discover. So, grab an old map, fire up QGIS, and start exploring! Just remember to take your time and pay attention to detail – the more accurate you are, the more valuable your results will be. Happy mapping!

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