Add polygon attributes to points VS join attributes by location. Joining polygon attributes to points is a pretty common geoprocessing step. There are multiple ways to solve the problem in QGIS, so I thought I’d have a look at how they perform. There is Join attributes by location in the Vector menu and Add polygon attributes to points in the Processing toolbox. My test data: Two shapefiles with 18,713 points and 17,397 irregular polygons. (Some system specs: 1.3GHz dualcore with 4GB RAM) And here are the results: This point clearly goes to Processing and the SAGA algorithm it provides access to. To measure execution time (in a very unscientific way), I just ran the tool from the python console using: Some notes of caution: SAGA comes readily installed in OSGeo4W.
Like this: Like Loading... QGIS 2.0 - Point in Polygon Query. Point in Polygon Query To find out how many points in a particular layer occur in polygons of a second layer, use this method. Points Layer For this exercise, we'll use the points showing railway stations in Taiwan, and the polygons for county level units in Taiwan. Our goal is to (a) calculate the number of railways station points in each county unit, and (b) create a thematic map of the results In QGIS, Add Vector Data, set UTF8 encoding, and browse to part_three/tw_stations.shp Add Vector Data, set BIG5 encoding, and browse to china/TW_POP.shp You should have two layers in your QGIS project: Checking and symbolizing results Close the attribute table, and right click on the layer to open the layer Properties Click on the STYLE tab to view the symbolization options On the upper left, change the Single Symbol drop-down option to GRADUATED.
After Clicking CLASSIFY, you should see the graduated symbols ramp You may customize your classification scheme in the Symbol, Range, and Label grid. QGIS 2.0 - CSV Import. Overview Prepare a table containing rows that include at least fields for: Unique ID, Latitude, and Longitude. Lat & Long values should be in decimal degree format (NOT degrees, minutes, seconds, format) Example of row with correct Lat & Long values: 23, Berlin, 52.500556, 13.398889 In the preceding example, 23 = unique ID for Berlin, Berlin = Placename, 52.500556 = Lat, 13.398889 = Long Save this table in Comma Seperated Values format (CSV) From Manage Layers Toolbar, use the Add Delimited Text Layer tool and select the CSV file to generate a points layer. Save the points layer to a Shapefile (or other format) for future use.
Preparing tabular data Tabular data can be developed in various spreadsheet applications. We reccommend LibreOffice for it's handling of specific language character set encodings. For our example, we downloaded the County File of Egyptian Placename Features from USGS Country Files. Add Delimited Text Layer Import CSV File Check points and attribute table. Using a QGIS spatial index to speed up your code · Nathan's QGIS Blog. 04 Jan 2013 If you need to do any kind of spatial operations in QGIS using Python or C++ you really want them to be as fast a possible in order reduce the amount of time you make the user wait. Lets take the simple scenario of a recent question that was asked on gis.stackexchange; Summing up values of neighboring polygons?. I went for the SQL approach as I like how quick SQL can express what you need to do, however SQL is not the only way to skin a cat as spatialthoughts has shown in his blog post. Here Ujaval has used Python to find the neighboring polygons of each feature.
In order to check if a feature touches another you need to have two features to compare against each other. So the above code is pretty simple, just loop each feature and check against every other feature. Note: We put all the features of the layer into a dictionary as it will make lookup quicker in the later index example. How can we speed up the above code? QgsSpatialIndex to rule them all Full code. Performing Spatial Joins — QGIS Tutorials and Tips. [ Download PDF A4 Letter ] Spatial Join is a classic GIS problem - transferring attributes from one layer to another based on their spatial relationship.
In QGIS, this functionality is available through the Join Attributes by Location tool. Overview of the task We will use 2 layers - A shapefile of burough boundaries of New York city and another shapefile of nursing home locations in New York city. We will use spatial join technique to find the total nursing home capacity for each of the buroughs. Other skills you will learn Deleting columns from the attribute table of a layer. Procedure Go to . Select the layer nybb.shp and click OK. Repeat the steps 3 and 4 for the another file OEM_NursingHomes_001.zip and load the OEM_NursingHomes_001.shp layer. Examine the attributes available for each feature.
Go to . The Target vector layer is the one we want to add the attributes to. Once the process finishes, select Yes when asked if you want to add the layer to TOC. Points in Polygon Analysis — QGIS Tutorials and Tips. [ Download PDF A4 Letter ] The power of GIS lies in analysing multiple data sources together. Often the answer you are seeking lies in many different layers and you need to do some analysis to extract and compile this information.
One such type of analysis is Points-in-Polygon. When you have a polygon layer and a point layer - and want to know how many or which of the points fall within the bounds of each polygon, you can use this method of analysis. Overview of the task Given the locations of all known significant earthquakes, we will try to find out which country has had the highest number of earthquakes. Procedure Open and browse to the downloaded signif.txt file. Since this is a tab-delimited file, choose Tab as the File format. Note You may see some error messages as QGIS tries to import the file. As the earthquake dataset has Latitude/Longitude coordinates, choose WGS 84 EPSG:436 as the CRS in the Coordinate Reference System Selector dialog. Click on. QGIS 2.0 - Spatial Join. Spatial Join A common GIS task is to join the attributes from one spatial data layer to another.
In this example we will join attributes from a polygon layer to a points layer, based on which polygon contains the points. Prepare Target Points Layer For this exercise, we'll use a set of points showing power plant sites in Taiwan from the CARMA database Add Vector Data, set UTF-8 encoding, and browse to part_three/Taiwan_CARMA_Xian80.shp Right click on the Layer in the Layer List and the General tab, to check the Coordinate Reference System (projection) for this layer Note that it is in Projected CRS, EPSG:2333. Cancel the Properties Dialog window. Target Points layer should be ready for the join Check Join Layer Now we want to Add Vector Layer and browse to the part_three/TW_POP.shp layer, encoding = big5 Click on the TW_POP layer in the layer list and drag it below the Taiwan_CARMA layer.
Reproject Join Layer Click OK or Cancel to close the Properties window. Run the Join. TypeBrewer. Colorbrewer: Color Advice for Maps. Overlays - Google Maps JavaScript API v3. You can add objects to the map to designate points, lines, areas, or collections of objects. The Maps JavaScript API calls these objects overlays. Overlays are tied to latitude/longitude coordinates, so they move when you drag or zoom the map. New Zealand Latitude and Longitude Map. Search | Roads and Addresses | GIS Data | LINZ Data Service. This table allows the application to check for invalid combinations of TLA, Electorate, Maori & 260 sheet references at the time of data entry. This table is recreated every time a new set of electoral boundaries takes effect, and is subsequently updated if new valid combinations are discovered.
This table is part of the Authoritative Streets and Places (ASP) Database. For more information about the database including the data model see here. Notes: This table contains a static unique identifier 'id' column that is not part of the original published ASP database. This column has been added to support incremental changesets on LDS.