Wednesday, November 20, 2013

We want to express the density in inhabitants / square km. E


Let's see how to create new fields in a Shapefile and perform calculations on them. This tutorial prolectrix soup maker is based on data previously processed in "Integration of a CSV file into QGIS." We have a table with all the attributes of census of the city of Bologna. prolectrix soup maker In each record, among other information present, there is the resident population ("POP_2001") and also the area of the relevant section ("SHAPE_AREA") expressed in square meters. If we want to know the distribution of the population on the territory of Bologna. We are interested then calculate the population density of each section by dividing the population on the area of interest.
From the table attributes "sezioni11" activate the "Edit mode" (Ctrl + E) by clicking on the pencil icon. Once activated mode we can proceed with "Open prolectrix soup maker the computer field" (Ctrl + I) by clicking the icon of the calculator. Activate the option "Create a new field" that will contain the result of the calculation. We call it "DENS_POP" and will be a decimal number with precision 1, which is a single digit after the decimal point.
We want to express the density in inhabitants / square km. E 'therefore necessary to divide by 10 ^ 6 the value of the area being stored prolectrix soup maker in square meters. The formula will then write: "POP_2011" / ("SHAPE_AREA" prolectrix soup maker / 1000000). We confirm and QGIS will perform the calculation for each section. At this point we exit the edit mode ricliccando on the button to save the new data and close the attribute table. To graphically display the results achieved, do a right click on "sezioni11" and select Properties> Style. From the drop-down menu at the top select the style "graduate". Under "Column" select "DENS_POP", while as a color scale we choose the one that seems most appropriate. In the classes we select a sufficient number of categories in which to discriminate the population density. You can add an additional class, with the button prolectrix soup maker "Add Class" to differentiate those sections that have density zero with a distinctive color such as white.
Congratulations on the quality of your explanations! Unfortunately I can not do the join of a vector because qgis 1.8 (windows) will not let me choose the fields. The drop-down menu carrier to be joined (join) gives no choice available (empty). where am I wrong?
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