QGIS tips

Expressions

Insert scale as an expression

In QGIS composer, set for the map an “Item ID” with value main_map and then in an expression in a HTML box or a Text box, you can insert the following expressions

[%'1 : '  || round(map_get(item_variables('main_map'), 'map_scale'),0)%]

Build HTML table from a layer

Insert in a box with HTML rendering the following

[%
concat(
  '<table>',
  '<thead><tr>Col 1 header</tr><tr>Col 2 header</tr></thead>',
  aggregate(
    layer:='my_layer',
    aggregate:='concatenate',
    expression:=concat(
      '<tr><td>',
      "col1",
      '<td><td>',
      "col2",
      '<td></tr>'),
    concatenator:=''
  ),
  '</table>')
%]

Do the same with filtering

[%
concat(
  '<table>',
  '<thead><tr>Col 1 header</tr><tr>Col 2 header</tr></thead>',
  aggregate(
    layer:='my_layer',
    aggregate:='concatenate',
    filter:="col1"='myvalue',
    expression:=concat(
      '<tr><td>',
      "col1",
      '<td><td>',
      "col2",
      '<td></tr>'),
    concatenator:=''
  ),
  '</table>')
%]

Do the same as first example but with ordering

Not aware of the way to order DESC, only with ASC behaviour

[%
concat(
  '<table>',
  '<thead><tr>Col 1 header</tr><tr>Col 2 header</tr></thead>',
  aggregate(
    layer:='my_layer',
    aggregate:='concatenate',
    expression:=concat(
      '<tr><td>',
      "col1",
      '<td><td>',
      "col2",
      '<td></tr>'),
    concatenator:='',
    order_by:=col1
  ),
  '</table>')
%]

Create points along line every n distance

This expression is intended to works at geometry generator level to avoid creating a second layer just to put intermediat points on top of a line layer

We use as distance of 5000 considering the layer use meters and is a line

collect_geometries(array_foreach(
generate_series(0, length($geometry),step:=5000),
make_point_m(
  x(line_interpolate_point($geometry, @element)),
  y(line_interpolate_point($geometry, @element)),
  @element)
))