gis basics - part ii
DESCRIPTION
AFTER THE TRAINING SESSIONS, YOU SHOULD BE ABLE TO:Create a basemap with a scale, legend, north arrow, base layers, and other elementsDownload and display data collected from your GPSCreate a vector file (specifically a .shp) from latitude and longitude coordinatesCreate a buffer around a polygonGeoreference an imageAttach attributes to geographically referenced dataMeasure distances between your data and the area of your polygonsTRANSCRIPT
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GIS BASICS 2
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AFTER THE TRAINING SESSIONS, YOU SHOULD BE ABLE TO:• Create a basemap with a scale, legend, north arrow,
base layers, and other elements• Download and display data collected from your GPS• Create a vector file (specifically a .shp) from latitude
and longitude coordinates• Create a buffer around a polygon• Georeference an image• Attach attributes to geographically referenced data• Measure distances between your data and the area of
your polygons
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RECAP: GIS BASICS PART 1
CONCEPTS1. What is GIS2. Coordinate Systems3. Data Types4. Where to Find Data
TUTORIAL ACTIVITY: Viewing Data1. Tour of QGIS2. Caramoan Municipal
Waters
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GIS BASICS PART 2CONCEPTS1. Vector Tools2. Raster Tools3. Digitizing4. Cartography
BASICS PART 35. GIS Field Skills6. Google Earth
TUTORIAL ACTIVITY7. Mapping Daraga 8. Vector Analysis9. Measuring Distance and
Area10.Making a Map (More
Elements)
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VECTOR TOOLS
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VECTOR TOOLS: GEOPROCESSING TOOLS
TOOL PURPOSE
CONVEX HULL(S)
Create minimum convex hull(s) for an input layer, or based on an ID field.
BUFFER(S) Create buffer(s) around features based on distance, or distance field.
INTERSECT Overlay layers such that output contains areas where both layers intersect.
UNION Overlay layers such that output contains intersecting and non-intersecting areas.
SYMMETRICAL DIFFERENCE
Overlay layers such that output contains those areas of the input and difference layers that do not intersect.
CLIP Overlay layers such that output contains areas that intersect the clip layer.
DIFFERENCE Overlay layers such that output contains areas not intersecting the clip layer.
DISSOLVE Merge features based on input field. All features with identical input values are combined to form one single feature.
BUFFER(S) Create buffer(s) around features based on distance, or distance field.
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VECTOR TOOLS: GEOPROCESSING TOOLS
BUFFER(S) Create buffer(s) around features based on distance, or distance field.
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VECTOR TOOLS: GEOPROCESSING TOOLS
TOOL PURPOSE
CONVEX HULL(S)
Create minimum convex hull(s) for an input layer, or based on an ID field.
BUFFER(S) Create buffer(s) around features based on distance, or distance field.
INTERSECT Overlay layers such that output contains areas where both layers intersect.
UNION Overlay layers such that output contains intersecting and non-intersecting areas.
SYMMETRICAL DIFFERENCE
Overlay layers such that output contains those areas of the input and difference layers that do not intersect.
CLIP Overlay layers such that output contains areas that intersect the clip layer.
DIFFERENCE Overlay layers such that output contains areas not intersecting the clip layer.
DISSOLVE Merge features based on input field. All features with identical input values are combined to form one single feature.
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VECTOR TOOLS: GEOPROCESSING TOOLS
CLIP Overlay layers such that output contains areas that intersect the clip layer.
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VECTOR TOOLS: GEOPROCESSING TOOLS
TOOL PURPOSE
CONVEX HULL(S)
Create minimum convex hull(s) for an input layer, or based on an ID field.
BUFFER(S) Create buffer(s) around features based on distance, or distance field.
INTERSECT Overlay layers such that output contains areas where both layers intersect.
UNION Overlay layers such that output contains intersecting and non-intersecting areas.
SYMMETRICAL DIFFERENCE
Overlay layers such that output contains those areas of the input and difference layers that do not intersect.
CLIP Overlay layers such that output contains areas that intersect the clip layer.
DIFFERENCE Overlay layers such that output contains areas not intersecting the clip layer.
DISSOLVE Merge features based on input field. All features with identical input values are combined to form one single feature.
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VECTOR TOOLS: GEOPROCESSING TOOLS
DISSOLVE Merge features based on input field. All features with identical input values are combined to form one single feature.
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VECTOR TOOLS: GEOPROCESSING TOOLS
TOOL PURPOSE
CONVEX HULL(S) Create minimum convex hull(s) for an input layer, or based on an ID field.
BUFFER(S) Create buffer(s) around features based on distance, or distance field.
INTERSECT Overlay layers such that output contains areas where both layers intersect.
UNION Overlay layers such that output contains intersecting and non-intersecting areas.
SYMMETRICAL DIFFERENCE
Overlay layers such that output contains those areas of the input and difference layers that do not intersect.
CLIP Overlay layers such that output contains areas that intersect the clip layer.
DIFFERENCE Overlay layers such that output contains areas not intersecting the clip layer.
DISSOLVE Merge features based on input field. All features with identical input values are combined to form one single feature.
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VECTOR TOOLS: GEOPROCESSING TOOLS
UNION Overlay layers such that output contains intersecting and non-intersecting areas.
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VECTOR TOOLS: GEOPROCESSING TOOLS
TOOL PURPOSE
CONVEX HULL(S) Create minimum convex hull(s) for an input layer, or based on an ID field.
BUFFER(S) Create buffer(s) around features based on distance, or distance field.
INTERSECT Overlay layers such that output contains areas where both layers intersect.
UNION Overlay layers such that output contains intersecting and non-intersecting areas.
SYMMETRICAL DIFFERENCE
Overlay layers such that output contains those areas of the input and difference layers that do not intersect.
CLIP Overlay layers such that output contains areas that intersect the clip layer.
DIFFERENCE Overlay layers such that output contains areas not intersecting the clip layer.
DISSOLVE Merge features based on input field. All features with identical input values are combined to form one single feature.
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VECTOR TOOLS: GEOPROCESSING TOOLS
DIFFERENCE Overlay layers such that output contains areas not intersecting the clip layer.
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VECTOR TOOLS: GEOPROCESSING TOOLS
TOOL PURPOSE
CONVEX HULL(S) Create minimum convex hull(s) for an input layer, or based on an ID field.
BUFFER(S) Create buffer(s) around features based on distance, or distance field.
INTERSECT Overlay layers such that output contains areas where both layers intersect.
UNION Overlay layers such that output contains intersecting and non-intersecting areas.
SYMMETRICAL DIFFERENCE
Overlay layers such that output contains those areas of the input and difference layers that do not intersect.
CLIP Overlay layers such that output contains areas that intersect the clip layer.
DIFFERENCE Overlay layers such that output contains areas not intersecting the clip layer.
DISSOLVE Merge features based on input field. All features with identical input values are combined to form one single feature.
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VECTOR TOOLS: GEOPROCESSING TOOLS
INTERSECT Overlay layers such that output contains areas where both layers intersect.
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VECTOR TOOLS: GEOMETRY TOOLSTOOL PURPOSE
CHECK GEOMETRY Check polygons for intersections, closed-holes, and fix node ordering.
EXPORT/ADD GEOMETRY COLUMNS
Add vector layer geometry info to point (XCOORD, YCOORD), line (LENGTH), or polygon (AREA, PERIMETER) layer.
POLYGON CENTROIDS
Calculate the true centroids for each polygon in an input polygon layer.
DELAUNAY TRIANGULATION
Calculate and output (as polygons) the delaunay triangulation of an input point vector layer.
VORONOI POLYGONS
Calculate voronoi polygons of an input point vector layer.
SIMPLIFY GEOMETRY
Generalize lines or polygons with a modified Douglas-Peucker algorithm.
DENSIFY GEOMETRY
Densify lines or polygons by adding vertices
MULTIPART TO SINGLEPARTS
Convert multipart features to multiple singlepart features. Creates simple polygons and lines.
SINGLEPARTS TO MULTIPART
Merge multiple features to a single multipart feature based on a unique ID field.
POLYGONS TO LINES
Convert polygons to lines, multipart polygons to multiple singlepart lines.
LINES TO POLYGONS
Convert lines to polygons, multipart lines to multiple singlepart polygons.
EXTRACT NODES Extract nodes from line and polygon layers and output them as points.
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VECTOR TOOLS: GEOMETRY TOOLSPOLYGON CENTROIDS
Calculate the true centroids for each polygon in an input polygon layer.
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VECTOR TOOLS: DATA MANAGEMENT TOOLS
TOOL PURPOSEDEFINE PROJECTION Specify the CRS for shapefiles whose CRS has not
been defined.JOIN ATTRIBUTES BY LOCATION
Join additional attributes to vector layer based on spatial relationship. Attributes from one vector layer are appended to the attribute table of another layer and exported as a shapefile.
SPLIT VECTOR LAYER Split input layer into multiple separate layers based on input field.
MERGE SHAPEFILES TO ONE
Merge several shapefiles within a folder into a new shapefile based on the layer type (point, line, area).
CREATE SPATIAL INDEX Create a spatial index for OGR supported formats.
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RASTER TOOLS: GEOREFERENCING
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RASTER TOOLS: GEOREFERENCING
UNCORRECTED IMAGE GEOREFERENC
ED/GEOMETRICALLY CORRECTED
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GEOREFERENCING: STEPS1. Add the raster dataset you want to georeference2. Add control points to link the raster dataset positions to known positions in map
coordinates3. Save the georeferencing information
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GEOREFERENCING: HOW DOES IT WORK?1. GCPs (Ground Control Points) are used to come up with a
formula to put the raster into the target coordinate system. Usually first order transformations will suffice unless data is very warped (then higher order is needed).
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GEOREFERENCING: HOW DOES IT WORK?2. Root Mean Square Error: the difference between the desired output coordinate for a GCP and the actual output coordinate for the same point, when the point istransformed with the geometric transformation.
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GEOREFERENCING: HOW DOES IT WORK?3. Resampling: Usually when you transform your raster, the cell centers of the input raster rarely line up with the cell centers on the output raster.
NEAREST NEIGHBOR
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GEOREFERENCING: HOW DOES IT WORK?3. Resampling: Usually when you transform your raster, the cell centers of the input raster rarely line up with the cell centers on the output raster.
BILINEAR INTERPOLATION
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GEOREFERENCING: HOW DOES IT WORK?3. Resampling: Usually when you transform your raster, the cell centers of the input raster rarely line up with the cell centers on the output raster.
CUBIC CONVOLUTION
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GEOREFERENCING: RESAMPLING
BILINEAR INTERPOLATION
NEAREST NEIGHBOR
CUBICCONVOLUTION
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RASTER TOOLS: RASTER CALCULATOR
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RASTER TOOLS: RASTER CALCULATORThe Raster Calculator allows you to perform calculations on basis of existing raster pixel values. The results are written to a new raster layer.
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RASTER TOOLS: RASTER CALCULATOR
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RASTER TOOLS: ZONAL STATISTICS
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RASTER TOOLS: ZONAL STATISTICS
You can calculate statistics in a raster layer according to zones, which are delineated by polygons. You can calculate the sum, the mean value and the total count of the pixels that are within a polygon.
ZONE RASTER VALUE RASTER
SUM = 0 + 1 + 3 + 1 + 0 = 5
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DIGITIZING
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DIGITIZING
Digitizing is one way we get data into GIS. There are three ways that digitizing is done in a GIS:1. Digitizing from paper maps2. Digitizing from existing GIS data3. Digitizing from scanned images uploaded into a GIS
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DIGITIZING
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DIGITIZING
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DIGITIZING: SNAPPING
If you set your snapping tolerance to 0.05 units, then it means that a point is snapped to an existing point if it comes nearer than 0.05 units.
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DIGITIZING: VERTICES
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DIGITIZING: ADVANCED
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CARTOGRAPHY
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CARTOGRAPHY: CRITICAL ELEMENTS
• Coordinate system (can also include datum)***• Title• Scale bar for each map frame you use• Map Legend• North Arrow• Information about the creation of the map (i.e.
When map was created, by whom, etc…)
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CARTOGRAPHY: VISUAL HIERARCHY
When placing elements of your map onto any kind of media, consider the visual hierarchy. That is, make the most important features most prominent by adjusting position, size, surrounding open space, color contrast, and line weights. Your most important data should be emphasized in the visual hierarchy. Boxes can help to elevate the visual hierarchy of the elements it surrounds.
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CARTOGRAPHY: OTHER NOTES
1. Color Choice2. Fonts3. Annotation/Labels4. Keep your audience in mind5. Media used to show your map (paper, web, etc…)6. Time and budget constraints
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QUESTIONS?