Each image has a grid. It is always present, but by default it is not visible until you activate it by toggling View → Show Grid in the main menu. If you want grids to be present more often than not, you can change the default behavior by checking "Show grid" in the Image Window Appearance page of the Preferences dialog. (Note that there are separate settings for Normal Mode and Fullscreen Mode.)

The default grid appearance, set up when you install GIMP, consists of plus-shaped black crosshairs at the grid line intersections, with grid lines spaced every 10 pixels both vertically and horizontally. You can customize the default grid using the Default Image Grid page of the Preferences dialog. If you only want to change the grid appearance for the current image, you can do so by choosing Image → Configure Grid from the main menu: this brings up the Configure Grid dialog.

Not only can a grid be helpful for judging distances and spatial relationships, it can also permit you to align things exactly with the grid, if you toggle View → Snap to Grid in the main menu: this causes the pointer to "warp" perfectly to any grid line located within a certain distance. You can customize the snap distance threshold by setting "Snap distance" in the Tool Options page of the Preferences dialog, but most people seem to be happy with the default value of 8 pixels. (Note that it is perfectly possible to snap to the grid even if the grid is not visible. It isn't easy to imagine why you might want to do this, though.)

Além da grade de imagem, o GIMP fornece também um tipo mais flexível de posicionamento auxiliar: as guias. Estas são linhas horizontais ou verticais, que você pode exibir temporariamente em uma imagem enquanto você está trabalhando nela.

To create a guide, simply click on one of the rulers in the image window and pull out a guide, while holding the mouse Left Button pressed. The guide is then displayed as a blue, dashed line, which follows the pointer. As soon as you create a guide, the “Move” tool is activated and the mouse pointer changes to the Move icon.

Você também pode criar uma guia com o comando Nova Guia, que permite colocar a guia precisamente sobre a imagem, o comando Nova guia (por percentagem)ou com o comando Novas guias a partir da seleção.

You can create as many guides as you like, positioned wherever you like. To move a guide after you have created it, activate the Move tool in the Toolbox (or press the M key), you can then click and drag a guide; click-and-drag the intersection of two guides to move them together. To delete a guide, simply drag it outside the image. Holding down the Shift key, you can move everything but a guide, using the guides as an effective alignment aid.

O comportamento das guias depende da opção de modo Mover da ferramenta de “Mover”, na caixa de “Opções de ferramenta”. Quando o modoCamada é selecionado, o ponteiro do mouse se transforma em uma pequena mão, logo que ele fica perto de uma guia. Em seguida, a guia é ativada e fica vermelha, e você pode mover a guia ou excluí-la movendo-ade volta para a régua. Se o modo de seleção, ou de Vetor está ativoselecionado, você pode posicionar uma guia, mas você não pode movê-la.

As with the grid, you can cause the pointer to snap to nearby guides, by toggling View → Snap to Guides in the main menu. If you have a number of guides and they are making it difficult for you to judge the image properly, you can hide them by toggling View → Show Guides. It is suggested that you only do this momentarily, otherwise you may get confused the next time you try to create a guide and don't see anything happening.

Se isso tornar as coisas mais fáceis para você, você pode alterar o comportamento padrão das guias na página de aparência da Janela Imagem da caixa de diálogo de Preferências. Entretanto, desativar a opção de Exibir as guias provavelmente não é uma boa ideia, pela razão acima.

Você pode remover as guias com o comando Imagem → Guias → Remover todas as guias.