QGIS training class 2

Geographic Information SystemQGIS Introduction(2)

microbase.LLChttp://microgeodata.com/

Agenda

W h a t ’s Q G I S ? B a s i c u s a g e B a s i c d a t a m a n a g e m e n t

S p a t i a l A n a l y s i s S p a t i a l d a t a a n d l i n g

G e o c o rd i n g C re a t e Ve c t o r d a t a A b o u t c o o rd i n a t e s y s t e m C re a t e K M L d a t a U t i l i z e O S M d a t a

Contents Today

2nd session

1 Spatial Analysis

2 Spatial Data handling

Homework

Lecture data

lecture1_data

tokyo23

homework2

1 Spat ia l Ana lys i s

1.1 Buf fer ing

A buffer in GIS is a zone around a map feature measured in units of distance or time. A buffer is often used for spatial analysis.

make 200m buffer polygons from a highway.

Add railway.shp in “tokyo23” folder and make 100m buffer polygons from the railways.tokyo23.

2 Input “100” in the form.

3) Check the checkbox of “Dissolve buffer results”.

->An optional dissolve can be performed to combine overlapping buffers.

1) Choose railway.shp as a vector data.

Vector > Geoprocessing Tool > Clip

A buffer polygon can be created from not only poline data but also point data and polygon data．

Exerc ise 1

Create 250m buffer polygon data from each station and save it as “station_buffer250.shp”.

ANSWER

Integrate features which locate in same extent.

seven elevenセブンイレブンの影

響圏

population in Meguro city seven eleven’s market scale

1 .2 Over lay

Various kinds of Overlay

Intersect Union Clip

Output

Inersectfeature

Unionfeature

Clipfeature

Output features have each attribute table of input features Just clip features

Meguro city can be selected by “Select layer by attribute” or “Select Features” from “ku.shp”.

Add “library.shp” and “ku.shp”. Clip libraries only in Meguro city.

Check the check box of “Use only selected features” and you can clip the target layer based on a clip layer which is selected.

Clipfeature

Overlay1: Clip

Vector > Geoprocessing Tool > Clip

Libraries in only Meguro city are clipped.

Intersect railways in Meguro ward using “library.shp” and “ku.shp”.Inersectfeature

Overlay1: Intersect

Vector > Geoprocessing Tool > Intersection

Check the check box of “Use only selected features” and you can clip the target layer based on a clip layer which is selected.

Railways in only Meguro city are intersected.

1) Choose following features only in Setagaya ward.• dentist.shp• station.shp• road.shp

2) Create following features in Setagaya ward.• 250m buffer polygons from each station.

Exerc ise2

dentist station road

ANSWER

1)Clip(or intersect) a dentist, a station and a road using “ku.shp” selecting Setagaya ward.

ANSWER

2) Dentists in the buffers are shown.

2 Spat ia l Data Handl ing

2.1Se lect Layer By Locat ion

Features can be selected by not only an attribute but also location.

ExampleSelect a dentist within 500m from a station

Select a ward which a highway go through.

Select a ward which borders on Meguro ward

Select a seven eleven in Meguro ward

Add “station.shp” and “dentist.shp” in “tokyo23” folder into layer. Choose a dentist within 500m from a station in Tokyo special districts.

Create 500m buffer polygons from each station.

Select a dentist within the buffers.

Choose a target layer in “selected features” and an overlapped layer in “intersect features”.

Vector > Research Tool > Select by location “Select by location” covers the following spatial relationship among features.

- within

- contain

Selected features color yellow.

The result show about 70% dentists locate in the place within 500m from station.

5129 in 6985 are selected. It may take a little while to select features.

Selected rows color blue in the attribute table.

If more advanced search methods than “Contains” and “Within” are required, the plugin “Spatial Query Plugin” will be useful.

- “Spatial Query Plugin” will appear if the checkbox in “QGIS Plugin Manager” is checked.

- Intersects A intersects B- Contains A contains B- Is disjoint- Equals A equals B- Overlaps A overlaps B- Crosses A crosses B- Touches A touches B- Within A within B

Vector > Spatial Query

1) Search the ward which intersect the highway.

2) Count the number of a supermarket within 250m from each station

using “station_buffer250.shp” created at Exercise1.

Exerc ise3

ANSWER

1) the borders which intersect highways.

467 shops

ANSWER

2) Count the number of a supermarket within 250m from each station.

2.2 Spat ia l Jo in

Joins attributes from one feature to another based on the spatial

relationship. The target features and the joined attributes from the join

features are written to the output feature class.

A cityshop

shop city

B city

C cityb

Add “convenience.shp” in “tokyo23” and save only “seven eleven” as “seven_eleven.shp”. Then join the attribute from “ku.shp” to it.

Check the checkbox of “Take attributes of first located feature”.

Vector > Data Management Tool > Join attributes by location

Attribute of “ku” is joined to “seven eleven”.

Attributes of “seven eleven” Attribute of “ku”

A city

shop sale

a 2500

b 3000

c 2000

d 1500shop sale city

a 2500 C市b 3000 A市c 2000 B市d 1500 B市

B city

C cityb

Join type varies depending on how joins between the target features and join features.

city number whole sale

A 1 3000

B 2 3500

C 1 2500

Main target

JOIN_ONE_TO_ONE

JOIN_ONE_TO_MANY

Add Census of commerce of 500m scale units

(H16_commerce.shp) and Census of population of block

scale unit(pop.shp). Then join the attributes from

“H16_commerce” to “pop”.

Exerc ise4

A block unit sometimes contains 500m grids and has more than 2 grids. Attribute summary should be “Take summary of interesting features.

If you want get an attribute value more accurately among different unit features, It would be one of the method to divide the value based on area of the features.

ANSWER

Another functions for spatial analysis are available.

��

)(1)(1

xf −= ∑=

)()(3)( 2 hxhxh

xK <−

= ��π

��

��!��

Spatial interpolation

Kernel density estimation

See geostatistics in more detail.・Kriging interpolation

・Sprine interpolation

・Spatial autocorrelation

etc...

Path Search

Shortest Path can be detected by Dijkstra method.

Service area analysis

Contents Today

2nd session

1 Spatial Analysis

2 Spatial Data handling

Homework

H O M E W O R K

homework2university.shp

highschool.shp

jr_school.shp

el_school.shp

firestation.shpfire station

elementaryschooljunior highschool

high school

college

Find the area thought to have high disaster risk in Tokyo special districts.

1) Describe characteristics and reasons of the area thought to have high disaster risk.

2) Create a map about 1) and paste it to your report.

<Hint>The data today and in “homework2” folder may be good for describing the disaster risk!

• population• population density• • school as rescue facility• elevation • public transpotation

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