# Manipulating the Attribute Table
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## Add field
- Add a field to the attribute table.
:::{Attention}
Depending on the information to be entered in the attribute field, the correct data type must be selected.
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:::{dropdown} Example: Add a field for population density, data type: Float or Double or Real (floating point numbers)
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## Delete field
- Delete a field from the attribute table.
:::{dropdown} Example: Delete all unused/unnecessary fields from the layer.
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## Calculate Field
- Calculate the attribute values for a field, e.g. based on the values of other fields.
- In QGIS you can create a new field or update an existing field.
:::{Attention}
Check if the data type of the field and your calculation match. For example, if you are calculating a ratio (e.g. density), the field should not be of type integer.
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:::{dropdown} Example: Calculate the population density using the already existing fields Population and Area.
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## Basic Statistics for Fields
- Generates a statistic for a specific field in the attribute table.
:::{dropdown} Example: Statistics for the field population density for all countries, what is the maximum value, average, etc.?
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## Statistics by Categories
- Create aggregated statistics for categories.
- For which fields in the attribute table should statistics be calculated?
- Which field in the attribute table contains the category?
:::{dropdown} Example: How many cities with more than 300,000 inhabitants are there per country? For each country: How many people live in the largest agglomeration?
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