The basic process of spatial data
Do not understand the spatial analysis can look at spatial data analysis concepts and QGIS data loading
Substantially common spatial data processing comprises cutting, merging, intersection, fusion, difference, intersection negated
Cut out
Overall Extraction and cutting element is overlapping the input element, it can be understood as FIG.
Our dining outlets in Shanghai address distribution as an example, can be divided into specific details (or less merge, intersection, integration, differential, intersection negated steps are similar to the following will not be repeated statement):
- Catering to load the data layers (layers waiting to be cut)
- Load the Shanghai administrative boundary layers (feature layers to be cut out)
- Click on the menu bar vector >> geoscience data processing tools >> Cutting
- Then 'pop cropping' vector layers in selected layers to be cut, cutting out the layer to select the trimming layer feature, the incoming file output address can be determined.
Also worth mentioning is that the toolbar can be used directly as a key can be cut in a layer region.
merge
The data of the same type of a plurality of input data sets into a new single set of input data, this tool can merge point, line, surface, or feature type table.
Below, similar to the above cutting step of cutting into the vector operations in the combined pattern, as shown below, and the Guangdong, Guangxi combined:
Intersection
Calculate the input feature geometric intersection. Portions of all layers and / or stacked with class feature elements or element to be written to the output feature class. Including two intersecting elements of the property
Merge
Based on the specified attribute polymerization feature
For example, according to the country's provinces and municipal administrative map integration
Features:
- There are specific attributes
- Suitable for surface data
The difference
By erasing the input polygon features and elements are superimposed to create a feature class, only the elements in the input portion other than the outer boundary of erase feature to copy the input feature class.
It can be understood as an eraser, erasing stacked section.
Intersection negated (symmetric split)
And updating the input feature elements are not reset elements or portions of elements to be written to the output feature class
Spatial data attribute selection and calculation
Select property sheet
Spatial data attribute is actually selected in QGIS data attribute data table of options to hot pot restaurants in Wuhan launched a spatial data table, for example:
In QGIS inside, using a large number of query operations are 'expression selecting feature' functions in the implementation, a query input calculation expression or the expression of the panel is opened, the corresponding data can be obtained, in a similar SQL client toolbar query panel functions end tools.
For example, we need to query taste score more than 9 points, and consumer hot pot restaurants in 60 yuan, enter the query '' ' "taste"> 9 AND "per capita" <60' '' can be quickly and accurately matched to meet the conditions the hot pot restaurants, and we can see where the distribution of these hot pot restaurants in Wuhan (yellow dot that is in line with the conditions of hot pot restaurants)
Calculated attribute table
Property sheet provides a very practical field calculator, we can update the original data in the original field of spatial data table, you can also add new fields. The following steps:
- Open the property sheet to select the field calculator
- Select the update operations is increased (i.e. Create or Update selection field choice, etc.)
- Setting field type, width, precision
- Enter the calculation statement and execution
For example, we still above Wuhan hot pot shop data, for example, to increase the overall score in the field attribute table.
After the field is calculated by the calculator operation, the attribute table can be seen that increasing the overall score of this field data
Of course, the calculation can be performed QGIS much more than in the field calculator, we can perform logic, time, mathematics, judgment conditions shown below, in many of the same functions and Python conversion method field, string functions, and the like operating.
Reproduced in: https: //juejin.im/post/5cfdbb466fb9a07ea9446397