arc misty vivid green - wordpress.com · 2014-12-04 · introduction to qgis - 2014/11/25 3 gis...

INTRODUCTION

TO

QGis

Introduction to QGis - 2014/11/25 2

Objectives

● Do some reminders on the concept of GIS and the types of manipulated data

● Discover the major components of the QGIS interface

● Learn how to change the basic settings


GIS

Definition:

● A Geographic Information System (GIS) is an information system capable of organizing and presenting alphanumeric data spatially referenced as well as produce plans and maps. It allows you to disseminate information on given phenomenon.

● The term refers to software tools (QGIS, MapInfo ...) to develop and operate a GIS.

● But the concept includes not only software! It also includes: data, equipment and know-how related to the use of GIS.


GIS

Features:

The main features of a GIS are:– Abstraction and representation of selected elements;– Data Acquisition;– Archiving;– Analysis of data to create new information;– View or card production.


The GIS data

Geographic data has four components:

– The geometric data refers to the shape and location of objects or phenomena;

– The descriptive data (or attribute) refers to the set of attributes

describing objects and phenomena;– Data styles refers to Display Settings objects (type of line,

color ...)– The associated metadata, that is to say, the data on the data

(Date of acquisition, owner's name, acquisition method ...).


The GIS data

Spatial Data Types: – Vector data are represented by points, lines, polygons– Raster data represent an image of a plan or a scanned photo:

- Scanned maps

- Aerial images

- Satellite Images

- DTM (Digital Terrain Model)

- ...


Coordinate system

● The ground coordinate system (datum and

projection) allows to position the objects relative to each other.

● official projection for Guyane:

RGFG95 UTM Zone 22N (EPSG code 2972)

● The WGS84 system is used by the GPS

● QGIS uses CRS sign (Coordinate Reference System)


Quantum GIS or QGIS

● GIS Software "Open source" developed by a community of developers for the treatment of geographic data.

● First version of QGIS release in June 2002.● QGIS Version 2.6.0 (released in November

2014).● http://qgis.org


Qgis interface


Qgis interfaceToolbar

● Right-click in the toolbar to display the list of toolbars available and choose the ones you want to display

● It is possible to set the position of the toolbars

SHIFTINGBAR


Qgis interface

Management of layers:● Set the visibility of the layer or not

● Change the stacking order of layers

● Enable access to properties of the layer

Double-click on the layer to access to the layer properties


Qgis interface

Window attribute data

● Display the attribute data of the layer

● Select records in a table

● Perform operations on the selection

● Change the values


Qgis interface

- General : defines the project options files, the appearance of layers default and the configuration of the window applications

- System : Set of system environment variables; added paths extensions to C ++ Additional

- Data Sources : management attributes and tables

- Rendering : defines the behavior and quality of rendering visible layers

- Colors : defines the standard colors of the style window for layers

- Canvas & Legend : defines the appearance of the map and legend layers

- MapTools : Sets the mode of identification layers, tools measurement, the zoom function and scale visualization

- Composer : defines the font and the characteristic grid of the composer

- Digitizing : Defines the settings of editing, snap mode and representation of vertices

- GDAL : list of different formats

- SCR : defines the reference coordinate system

- Locale : defines the parameters of the location (system and language)

- Network : defines the parameters of Proxy for internet access

● Setting default QGIS interface● Settings / Options


Qgis setting

● Settings / Options / CRS

Automatic reprojectionof layers

Projection for new projects

Projection for new layers


Qgis setting

Parameters and units of measure

Zoom parameters

Predifined scale


Working resources

● Supported formats:

- Vector: ESRI shapefiles (.shp), MapInfo tables (.tab), KML, DXF

- Raster: aerial photographs, satellite images, funds map scanned, Digital Terrain Models (DTM)

- Tables database with a spatial support enabled: PostgreSQL / PostGIS, SQLite / SpatiaLite

- Data Online (Internet / Intranet) via WMS or WFS protocols

● Toolbar “Layers control”:

● Add a vector layer

● Add a raster layer

● Add a PostGIS layer

● Add a layer Spatialite

● Add a layer MSSQL

● Add an Oracle Spatial layer

● Add a WMS layer

● Add a layer WCS

● Add a WFS layer

● Add a layer delimited text

● New Shapefile layer


Control of layers

Other functions of the layer manager:

– Display properties with a right-click → Properties, or double-click

– Move selected layer with drag and drop

– Renaming a layer with a right-click → Rename (This function does not change the file name, it is only for display and the legend on the impression of the card)

Point vector layer

line vector layer

Polygon vector layer

Raster layer

Visibility or not of layer

Create group of layers

Delete a layer

Send up a layer

Send down a layer


Properties of layer

Select the layer and right-click on "Properties" (or double-click on the layer)

→ Allows you to change the display name, specify the SCR

→ Change the appearance of the layer

→ Label the layer in an attribute table field

→ View the attribute table

→ Simplify geometry to accelerate the rendering

→ Properties tooltips (changing the display field)

→ Perform actions based on the attributes of an entity

→ Join another layer from a common attribute field

→ Add diagrams based on attribute fields

→ type layer, the path layer


Properties of layer

Displayed name of layer

Change the projection

Show layer depending on the scale


Attributes

●Toolbar “Attributes”

➔ Identify entities or examine an object

➔Perform action of the entity

➔graphic Selection (one or more entities)

➔Uncheck all entities

➔Select entities by using an expression

➔Open the attribute table

➔Open field calculator

➔Measurement (length, area, angle)

➔Tooltips

➔New Bookmark

➔Show bookmarks

➔Annotation


Style managementvector

Symbol rendering :- single- Categorized- Graduated

Style properties

Layer rendering

Style modification

Loading a style file

Saving styleassociated with the table

Saving in a style file


Style managementraster

Render Type(single band or 3color bands)



Render Type "Singleband gray"

● Layers 'images' color that you want to display in black and white



Render Type "Singleband pseudocolor"


Digitizing

● Create a new shapefile layer

Type of vector

Choice of projection layer

Name and type of new attribute field

Naming and saving of the layer


Polygon digitizing

● Switch the layer in edit mode

● Draw a new polygon and fill attributes (right-click to complete the polygon)

Polygon tool

Attributes seizure:

● Once the digitizing is complete: - Save the changes of layer

- Stop mode edition


Digitizing complement

● Menu settings / Snapping options

Snapping layer

Research radius


Practical exercises

● Set CRS (WGS84) and units (meter) of QGIS.

● Open the raster layer IMAGERY_demo_687_340 (in the file Training_session_QGIS\Raster) and the vector layers REMARKABLE_POINT, WATER_SYSTEM and TOWN (in the file Training_session_QGIS\Raster).

● Change the style of this layers for an adequat symbology.

● Create a new shapefile layer (polygon), name it French_guiana and save in Training_session_QGIS\Intro_backup.

● Set the options to snap the layer TOWN.

● Digitize the outline of the French Guiana and save.

.


Joins

Add a join

Select the layer to join

Select the common fields to join the both layers

Delete a join

Choice the field who will appear in the join

● Double-clic / Layer properties / Joins


Field calculator

Create a new field Update existing field

Name of the new fieldChoice the field to update

Data type of the new field

Function list

Expression to create or to update the field

● Right-click on the layer / Open attribute table / Field calculator


Spatial query● Install the Spatial query plugin in menu:

Check the spatial query case


Spatial query

● The “spatial query” tool is enable to create a selection by combining data from two vector layers.

● This spatial query creates a selection of the towns who contain any roads: ● There are 15 towns who contain any roads:

Create a new vector layer from the selected towns


Attribute query

● To create a selection by attribute:

In the attribute table, click on Select by expression.

And tape the query.


Practical exercises

● Open the vector layer BOUNDARY (Training_session_QGIS\Shape).

● Join the layer TOWN and the layer BOUNDARY by the field ID_BDCARTO.

● With the Field calculator of the layer TOWN, create a field DENS_POP (population density: population / superficie).

● With Spatial query, select the towns who contain remarkable points.

● Create a selection of town that have more than 10 000 inhabitants.

arc misty vivid green - wordpress.com · 2014-12-04 · introduction to qgis - 2014/11/25 3 gis...

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