Automatizarea Creării Hărților cu ajutorul Atlasului (QGIS3)¶

Dacă organizația dvs. imprimă hărți sau le publică online, apare adesea nevoia de a crea unele hărți pe baza aceluiași șablon - de obicei câte unul pentru fiecare unitate administrativă sau regiune de interes. Crearea manuală a acestor hărți poate fi consumatoare de timp, iar dacă acestea necesită actualizare periodică, atunci totul se poate transforma într-o adevărată corvoadă. QGIS dispune de un instrument numit Atlas care vă poate ajuta să creați un șablon, pe baza căruia să publicați cu ușurință un număr mare de hărți, pentru diferite regiuni geografice. Dacă nu sunteți familiarizați cu elementele de bază privind Paginarea Compozițiilor, puteți parcurge tutorialul Crearea unei Hărți.

Privire de ansamblu asupra activității¶

Acest tutorial vă arată cum să creați harta zonelor mlăștinoase pentru fiecare regiune din statul Hawaii.

Alte competențe pe care le veți dobândi¶

Utilizarea stilului de randare Poligoane Inversate pentru umplerea zonelor din afara poligoanelor.
Scrierea unei expresii folosind stilul de randare Bazat pe Reguli, în scopul afișării doar a entității curente din Atlas.
Scrierea unei expresii dedicată creării de etichete dinamice în modulul de Paginare a Compoziților.
Utilizarea stilului de umplere Shapeburst la umplerea bitonală a poligoanelor.

Obținerea datelor¶

Vom folosi Straturile de Date GIS din Statul Hawaii - Biroul de Planificare

Descărcați stratul de `Zone umede http://files.hawaii.gov/dbedt/op/gis/data/HI_Wetlands.shp.zip>`_ din categoriile Biologică și Ecologică.

Descărcați stratul Limitelor recensământului regional 2010 din categoria Cultură și Demografie.

Pentru comoditate, puteți descărca direct o copie a ambelor seturi de date, accesând linkurile de mai jos:

HI_Wetlands.shp.zip

county10.shp.zip

Sursa de date: [HAWAII]

Procedura¶

Locate the HI_Wetlands.shp.zip file in the QGIS Browser and expand it. Select the HI_Wetlands_Poly.shp file and drag it to the canvas. This layer contains polygons representing wetlands in the entire state of Hawaii.

Since we want to make separate wetlands map for each county in the state, we will need the county boundaries layer. Browse to the county10.shp.zip file and expand it. Select the county10.shp file and drag it to the canvas.

Turn off the visibility of the HI_Wetlands_Poly layer temporarily. You will see the polygons from the county10 layer clearly now. There are 5 features contained in this layer, with each feature having 1 or more polygons associated with it. The features represent 5 counties. We will use this layer as the coverage layer and configure QGIS to create 5 separate maps - one for each feature - automatically.

Turn on the visibility of the HI_Wetlands_Poly layer. Go to Project ‣ New Print Layout...

Lăsați necompletat titlul compoziției, apoi faceți clic pe OK.

In the Print Layout window, go to Layout ‣ Add Map.

Drag a rectangle while holding the left mouse button where you would like to insert the map.

In QGIS3, the Atlas tab is not visible by default. Select View ‣ Panels ‣ Atlas.

Switch to the Atlas tab. Check the Generate an atlas box.

Select the county10 as the Coverage layer. This will indicate that we want to create 1 map each for every polygon feature in the county10 layer. You can also check the Hidden coverage layer so that the features themselves will not appear on the map.

Switch to the Item Properties tab. Scroll down and check the Controlled by atlas box. This will indicate the layout that the content of the map displayed in this item will be determined by the Atlas tool.

Notă

You must enable the Generare an atlas box in the Atlas tab, otherwise the Controlled by atlas checkbox will be diasbled.

Now that you have configuring the Atlas settings, go to Atlas ‣ Preview Atlas.

You will see the map refresh and show how individual map will look like. You can preview how the map will look for each of the county polygons. Go to Atlas ‣ Next Feature. Atlas will render the map to the extent of the next feature in the coverage layer.

Let’s add a label to the map. Go to Layout ‣ Add Label.

Under the Item properties tab, locate the Main properties section and click Insert an Expression… button.

The label of the map can use the attributes from the coverage layer. The concat function is used to join multiple text items into a single text item. In this case we will join the value of the NAME10 attribute of the county10 layer with the text County of. Add an expression like below and click OK.

concat('County of ', "NAME10")

Delete the leading Lorem ipsum placeholder text so that the textbox contains only the expression. Scroll down to the Appearance section and click on the Font dropdown. Choose the font and adjust the size to your liking.

Choose Center as the Horizontal alignment and Middle as the Vertical alignment option.

Add another label and enter Wetlands Map under the Main properties. Since there is no expression here, this text will remain the same on all maps.

Go to Atlas ‣ Last Feature and verify that the map labels do work as intended. You will notice that the wetland map has polygons extending out in the ocean that looks ugly. We can change the style to that areas outside the county boundaries are hidden.

Switch to the main QGIS window. Right-click the county10 layer and select Properties.

In the Symbology tab, select the Inverted polygons renderer. This renderer styles the outside of the polygon - not inside. Select white as the fill color and click OK.

You will notice that the polygons extending outside of the county boundaries are now disappeared. In reality, they are hidden by the white color fill extending out from the county polygons because of the Inverted polygons style.

Switch to the Layout window. If we want the effect of the inverted polygons to show, we need to uncheck the Hidden coverage layer box under Atlas tab. Once unchecked, the rendered image will appear clean and areas outside the coverage polygon is not visible.

There is one more problem though. You will notice that in some cases, parts of the map that are outside the coverage layer boundary are still visible. This is because Atlas doesn’t automatically hide other features. This can be useful in some cases, but for our purpose, we only want to show wetlands of the county whose map is being generated. To fix this, switch back to the main QGIS window and right-click the county10 layer and select Properties.

In the Symbology tab, select Rule-based as the Sub renderer. Double-click the area under Rule.

In the Edit rule dialog, click the Expression button next to Filter.

In the Expression string builder, expand the Variables group of functions. The @atlas_featureid variable stores the id of the the currently selected feature. We will construct an expression that will select only the currently selected Atlas feature. Enter the expression as below and click OK.

$id = @atlas_featureid

Close all intermediate dialogs and switch back to the Layout window. Select Map 1 item and click the Update preview button under Item properties tab to see the changes. Notice that now only the area covering the county boundary is shown.

Notă

If you do not see the Update preview button, it may help to select another Item element first and then select Map 1 again.

We will now add another dynamic label to show the current date. Go to Layout ‣ Add Label and select the area on the map. Click Insert an expression button.

Expand the Date and Time functions group and you will find the $now function. This holds the current system time. The function todate() will convert this to a date string. Enter the expression as below and click OK.

concat('Created on: ', todate($now))

Add another label citing the data source. You may also add other map elements such as a north arrow, scalebar etc. as described in Crearea unei Hărți tutorial.

We will make one last styling improvement. Switch back to the main QGIS window and right-click the HI_Wetlands_Poly layer and select Properties.

In the Symbology tab, click on Simple fill and select Shapeburst fill as the Symbol layer type. Choose the Two color option and select shades of green and blue that you like. Click OK.

Select Map 1 item and click the Update preview button under Item properties tab to see the changes.

O dată ce vă place aspectul hărții, accesați Atlas ‣ Exportare Atlas sub formă de Imagini.

Selectați un director de pe calculatorul dumneavoastră, apoi faceți clic pe Alegere.

Leave the default options in the Image Export Options and click Save.

Instrumentul Atlas va parcurge fiecare element din stratul de acoperire, după care crea imagini separate ale hărții, pe baza modelului creat. Puteți vedea imaginile în director, o dată ce procesul s-a încheiat.