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I have a map of an area, have created a vector grid over this, and want to score different areas of the map by risk (high risk, medium risk, low risk), by scoring each cell. I want to define these areas by drawing them in.

Is it possible to divide up a vector grid into different sections by defining them manually?

I am using QGIS version 2.18.24.

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To assign a risk level to each grid cell:

  1. Add a new field to the attribute table.

    • Type: Text (string)
    • Length: at least 6 (This is the number of characters that will fit in the field; if the longest word will be "medium" you only need 6 characters. Make it longer if you plan to use longer words/phrases, eg "medium-high")

    enter image description here

  2. Select the low-risk cells, and update their "risk_level" values to 'low'. Repeat for medium-risk and high-risk cells. Or edit the field value for each feature individually.

    enter image description here

  3. Optional: Visualize the risk levels on the map with a categorized style.

    enter image description here

    Tip: a red-yellow-green color scheme like the one in my example is not colorblind-friendly. Use the various preview modes (available through the View menu) to check how your map will appear.

  4. Optional: Use the Dissolve tool to merge cells based on their risk level. This will give you one multi-part polygon for the low-risk areas, one for the medium-risk areas, and one for the high-risk areas.

    enter image description here enter image description here

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