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FOREST ECOSYSTEM: GOODS AND SERVICES
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T.V. Ramachandra Subash Chandran M.D. Bharath Setturu Vinay S Bharath H. Aithal G. R. Rao |
Energy & Wetlands Research Group, Centre for Ecological Sciences,
Indian Institute of Science, Bangalore, Karnataka, 560 012, India. E Mail: tvr@iisc.ac.in; Tel: 91-080-22933099, 2293 3503 extn 101, 107, 113 |
QUANTUM GIS (QGIS) – SPATIAL MAPPING TOOL
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QGIS (http://qgis.org) is a Free and Open Source Geographic Information System for manipulating geographical data (vector, raster), statistical analysis. QGIS project was initiated on May of 2002 by Gary Sherman, established as a project on SourceForge. The first release was on July 19, 2002 and QGIS 3.0.0 'Girona' as the current version. QGIS is multiplatform GIS that runs on Windows, Unix, Linux platforms, macOS and Android. QGIS is a user-friendly GIS (https://www.qgis.org/en/site/forusers/download), providing common functions and features supports a number of raster and vector data formats. The plugin architecture provides access to new format support easily. QGIS is released under the GNU General Public License (GPL).
Installation:
Each session can be saved as a “Project”. The Print Composer helps in styling output images and saving thematic maps with layout and legends.
The following shows the different options available under each menu.
Working with Vector data
Vector files can be point, line, polygon forms store a description about any feature. QGIS support numerous vector data formats (Shape File, KML, Tab, MIF etc.). The most commonly used format is ESRI Shape File. To input vector data, click on Layer, then Add vector layer. Locate the vector file stored in your system, select “Filename.shp”, then vector feature will be loaded. You can change projection by right click properties or save as option to save a new file with you own projection. The global default CRS is EPSG:4326 - WGS 84 (proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs). Options for global and project-wide CRS (Coordinate Reference System) for layers allows to define custom coordinate reference systems and supports on-the-fly (OTF) projection of vector and raster layers - Can display layers (with different CRS) and options for overlay. QGIS supports >2,700 known CRS. Definitions for each of these CRS are stored in a SQLite database that is installed with QGIS.
The selected vector file will be displayed as,
To improve performance then Right click on layer name select properties you will get options as, General, Styles, Labels, Attributes, Metadata, Actions, Joins, Diagram overlay.
Database ingest-querying:
Data ingestion is the process of obtaining, importing, and processing data. Process involves altering individual files by editing their content and fit into a larger document. Load vector file (Ex: IISc buildings shape file to see the Querying feature in QGIS).
Right click on Layer name and click Open Attribute Table
Attribute Table will be displayed with features already stored in the database. To compute area of buildings, click on Start editing (Pencil type icon) and click on Mapcalculator.
Add filed data type to be created to store data. Since Area is real value provide data type as Real with 2 precision width. Locate $Area under predefined Geometry functions. Click on it and press OK then Area will be computed stored in the Area column.
Creating Thematic Maps: Right click on BBMP Wards Vector file and see the attribute table byclicking Open Attribute Table. The layer has details such as Ward Name, Ward No, Population Male, Poulation Female, SC and ST population, Total Population etc. If we want to represent the Wards having population greater than 15000 and other categories in different colors, we use thematic map representation. Close Attribute Table. Right Click on Vector file name, click on Properties. Then Properties menu will show various options, click on Styling tool bar then by default Single Symbology will be shown click on that tab it will show the various options such as Single Symbology, Categorized, Graduated etc. Select on Graduated option. Then specify the column name to be used for Thematic map creation. Select Total Population column then click on Classify by default it will show 5 categories. If you want to reduce or increase you can specify. If you want your own ranges to be displayed click on the row1 and specify maximum break for each row. You can click on color symbol to change required color. You can also edit legend entry text to be shown as you wish. After all changes press Apply and click OK. Then the final output will be shown in Map Display.
Use print composer option under Project section to save as JPG/PNG output file formats with Legend and Scale bar details.
Print composer has
● Apply map, legend, north arrow and text
● Using external programms (inkscape) for finetuning.
● Lots of paper formats supported; Separate DPI settings
● Logo inclusion, legend, labels, northarrow
● PNG/SVG/PDF support; Adjustable drawing scale
Dissolve: Dissolve tool is used to create a single vector boundary from a multiple vector files. For ex. we have provided BBMP ward boundaries file, to have a single BBMP boundary (Outer) then we will use Dissolve tool. For specifying a common field Right click on Layer name, Open Attribute Table. Click Toggle Editing then click on MapCalculator. Create a new field name as NewId, datatype as Integer. Just Type 1 in command operation section. Then a new field such as NewId has been created with all columns having Id as 1. Now stop Toggle Editing then save edits.
Click on Processing load tool box type “Dissolve”, then Dissolve tool will be shown under Vector Geometry operations section. Click on Dissolve tool then Dissolve tool GUI will be opened. It asks to load vector file input then indicate the filed to be dissolved. Click RUN to dissolve operation, then output will be shown.
Interpolation: Interpolation is used to create continuous surface from discrete points. It is a process of using points with known values to estimate values at other unknown points. A lot of real world phenomena are continuous - elevations, soils, temperatures, rainfall etc. If we wanted to model these, it is impossible to take measurements throughout the surface. Hence, the field measurements are taken at various points along the surface and the intermediate values are inferred by a process called ‘interpolation’. In QGIS, interpolation is achieved using the built-in Interpolation plugin. First import vector file or CSV file to be interpolated. If you are importing CSV then save it as Vector file.
Importing CSV file
Then save as ESRI Shape file with “UTM Projection” by right click on layer name SaveAs Option.
Importing Vector file
Click Raster option in Menu bar then click Interpolation and Interpolation. Provide Vector file name and column to be considered, raster cell size (30 m) and output file name.
Run Zonal Statistic option available under Raster toolbar to compute ward wise Mean Rainfall.
Importing Google earth data:
Working with Raster data:
Geo referencing
Digitising features (vector data) from Raster data:
Digitising features (water bodies) from Topo map:
Help from QGIS:
QGIS has active community support, update and upgrades
http://wgbis.ces.iisc.ernet.in/biodiversity/
http://www.qgis.org/en/site/forusers/index.html#
http://www.qgis.org/en/docs/index.html
http://wgbis.ces.iisc.ernet.in/grass/
http://wgbis.ces.iisc.ernet.in/foss/
http://wgbis.ces.iisc.ernet.in/energy/water/paper/researchpaper2.html#f
http://wgbis.ces.iisc.ernet.in/biodiversity/pubs/ETR/index.htm
Contact Address : | |||
Dr. T.V. Ramachandra Energy & Wetlands Research Group, Centre for Ecological Sciences, New Biological Sciences Building, 3rd Floor, E-Wing, Lab: TE15 Indian Institute of Science, Bangalore – 560 012, INDIA. Tel : 91-80-22933099 / 22933503(Ext:107) / 23600985 Fax : 91-80-23601428 / 23600085 / 23600683 [CES-TVR] E-mail : tvr@iisc.ac.in, energy.ces@iisc.ac.in, Web : http://wgbis.ces.iisc.ernet.in/energy |