1. Topic 1. Using PostGis To Manage Your GIS Data

2. Outline Part1. Brief Introduction of PostGIS and Why do we need it?
Part2. Install PostgreSQL, PostGIS and Tools
Part3. Load Data into PostGis Tables and Connect Q-GIS with PostGis
Part4. Simple Query
Part5. Geometry and Spatial Relations

3. Part1. Brief Introduction of PostGIS and Why we need it?

4. How we store and use our own geometric data
A GIS-data record that we collected by ourselves usually looks like:
place name or title
Releated metadata: (category, background information, other notes, comments, descriptions. )
GeoReference (longitute and latitue values)
Example:
Place Name：法鼓山世界教育園區 (DDM World Center for Buddhist Education )
Category: Buddhism, Temples, Eductaion
GeoReference: ,
There are usually highly structured data, therefore, we usually save them in a spreadsheet.

5. An SpreadSheet Example

6. Then, we put them into QGIS
EXCEL -> CSV -> QGIS

7. Disadvantages of spreadsheet (I)
EXCEL(spreadsheet application) is not design for managing large amount data.
It doesn’t scale. As the amount of data increases, performance suffers, and the visual interface becomes a liability instead of a benefit. It also has fixed limits on how big a spreadsheet and its cells can be.
It lacks data integrity. Because every cell is a unique snowflake, things can get very inconsistent

8. Disadvantages of spreadsheet (II)
It’s not very good for working with multiple datasets in combination.
Collaborating and sharing is hard. It’s hard to control versions and have a “master” set of data, especially when many people are working on the same project (Google Spreadsheets fix some of this).
EXCEL doesn't support geometric objects, and provides no function for manipulate geometric data.

9. Relational DataBase Management System
We need a better data management tool than EXCEL when the amount of data becomes larger and more complex.
Generally speaking, we will use Relational DataBase Management System (RDBMS) to replace EXCEL as the main data management system.
The same is true for the development of GIS system.

10. Development of GIS System (I)
Frist Generation GIS: GIS Tools + Data saved in backend proprietary format data file.
This architecture lacks of the ability to work with others.

11. Development of GIS System (II)
Second Generation GIS: The backend data become a hybrid architecture. The geometric objects are store in proprietary format data file.
Other information are store in a DBMS
EX: ESRI shape format, the feature geometry is stored in .shp, .shx, other attributes are stored in .dbf (RDBMS) file.

12. Development of GIS System (III)
Third Generation GIS: The backend data is now saved to a Spatial Database. (ex: ArcGIS, QGIS)
Some other advanced data management function provided by a database:
Support SQL command, able to cooperate with other system like: web application
Concurrency Control: allow multiple users working on the same data set.
User Privilege Management
Complete Backup solution
…..

13. What is Spatial Database
Spatial databases = Traditional RDBMS + modules/Data Type Definitions/functions to store and manipulate spatial objects
Defining Spatial data types referring to shapes such as point, line, and polygon;
Able to build Multi-dimensional spatial indexing for efficient processing of spatial operations;
Built-in Spatial functions, posed in SQL, for querying of spatial properties and relationships.

14. Common Spatial Databases
Oracle Spatial and Graph
Based on Oracle Database, Proprietary and very expansive
MS-SQL Databse: Proprietary and quite expansive
MySQL/mariaDB spatial, opensource
PostGIS
Based on PostgreSQL, opensource (most recommend)
Spatialite
Based on sqlite, opensource
SpatiaLite is probably the best choice when the project at hand needs a standalone, embedded database. Lets say for example you are building a mobile or desktop application that requires an embedded database.

15. What is PostGIS + =
Least version:
Least version:

16. Part2. Install PostgreSQL, PostGIS
and Tools

17. Brief Procedure of PostGIS Installation
Install softwares:
PostgreSQL 9.6.x
PostGIS 2.3.2
pgAdmin III 1.2.2
Perform post-install configuration for MAC/Ubuntu
Use pgAdmin3 to connect server
Create first spatial Database
Activate PostGIS extenation

18. Install PostGIS – windows (1/3)
Install: postgresql windows-x64.exe
Set Superuser Password
Skip Stack Builder

19. Set Password for "postgres"
Postgres is the default superuser for postgreSQL database. During the installation, you will ask to set the password for postgres.
Please remember password of postgres, it is important for following steps.

20. Install PostGIS – windows (2/3)
2. Install: postgis-bundle-pg96x64-setup exe

21. Install PostGIS – windows (3/3)
Extract and Install: pgadmin zip

22. Install PostGIS -- MAC Extract and Install: Postgres-9.6.3.zip
(PostgreSQL PostGIS 2.3.2)

23. Install pgAdmin3 Extract and Install: pgadmin3-1.22.2.zip
Drag to Applications Folder

24. First time open pgAdmin 3
Right Click

25. Configure PostgreSQL Database --MAC
After installing postgresSQL, postGis and pgAdmin, you still need to configure the database before we can really use it.
The post-install configuration of postgresSQL in MAC OS system is a bit more complicate than windows and Linux.
We need performs following 3 commands under terminal.

26. Post Installation (I) --MAC
Step 0. Run Terminal
Step 1a. in order to use the command line tools delivered with Postgres.app, execute the following command in Terminal to configure your $PATH
> sudo mkdir -p /etc/paths.d && echo /Applications/Postgres.app/Contents/Versions/latest/bin | sudo tee /etc/paths.d/postgresapp
Password is required
Step 1b. Close and Restart Terminal

27. Post Installation (II) --MAC
Step 2. Create superuser account: postgres
> createuser -s postgres
If no error message is shown on the screen, then you succeeded.
If you see:
createuser: creation of new role failed: ERROR: role "postgres" already exists
That is fine, too.
But If you see:
-bash: createuser : command not found
You probably: 1. didn't enter correct command of step1. or 2. forget closing and restarting terminal.

28. Post Installation (III) --MAC
Step 3. execute psql and set password for user postgres
> psql
Your-account=# \password postgres
Enter new password: (password for postgres)
Enter it again: (password again)
Please remember password of postgres, it is important for following steps.
If you see:
ERROR: role "postgres" does not exist
You didn't create postgres in step 2, leave psql, and run step2 again.
Command for exiting psql:
Your-account=# \q

29. Install PostGIS -- Ubuntu
Run following command
> sudo apt-get install postgis postgresql-contrib pgadmin3
After installation complete, run following command
> sudo -i -u postgres psql
postgres=# \password
Enter new password:
Enter it again:
postgres=# \quit
For setting password of postgres

30. Using pgAdmin III to Connect postgreSQL Server
Windows
MAC OS X
Ubuntu

31. Register New Server first open pgAdmin, you must Register a new Server
Click here to Register
a new Server

32. Register New Server (II)
Name:
Local PostgreSQL
Host:
localhost
Password:
Password of postgres OK

33. Connect to 「Local postgreSQL」
Click the new "Local PostgreSQL" entry to connect

34. Databases
Click "Databases" under Local postgreSQL, you will see a "postgres" databases already existed in your system.
We now need to create a Database for this course.

35. Creating a Spatial Databases
Right click the databases entry, you will see a menu pop-up. Click "New Database…" in the popup menu.

36. New Database Diaglog
Name:
TaiwanBuddhistTemples
Owner:
postgres OK

37. Explore "TaiwanBuddhistTemples" Database
Select the new TaiwanBuddhistTemples database and open it up to display the tree of objects.
You’ll see the public schema under TaiwnBuddhistTemple s > Schema > Public.

38. Activate PostGIS function
Need to run a Query to load the PostGIS spatial extension.
Click
Selected

39. Running SQL Command CREATE EXTENSION postgis;
Make sure 'TaiwanBuddhistTemples' is selected
CREATE EXTENSION postgis;
CREATE EXTENSION postgis_topology;
Click the Play button in the toolbar (or press F5) to “Execute the Query.”

40. Checking PostGIS Installation
Make sure 'TaiwanBuddhistTemples' is selected
SELECT postgis_full_version();
PostGIS_Full_Version: Reports full PostGIS version and build configuration info.
Execute the query. You shall see:

41. Part3. Load Data into PostGis Tables and Connect Q-GIS with PostGis

42. Loading Spatial Data into Tables
We have prepared several datasets, the all stored in the dataset folder:
D1: Boundary of 368 Taiwanese Towns (shape file)
D2: MRT Lines (shape file)
D3: Location of MRT Stations (shape file)
D4: Population of 368 Taiwanese Towns (Excel)
D5: Location of Taiwanese Temples (Excel, with locations)
For windows users, please make sure the "DataSet folder" is not stored under the folders with Chinese Characters.

43. Loading Shape Files (Using pgShapeLoader)
Works for Windows/Ubuntu
Using pgShapeLoader application
Windows 7
Ubuntu: shp2pgsql-gui

44. pgShapeLoader Applicaion
User Name:
postgres 1
Password:
Password of postgres
Database:
TaiwanBuddhistTemples 2
Connecting: host=localhost port=5432 user=postgres password='*******' dbname=TaiwanBuddhistTemples
Connection succeeded.

45. For D1: Table: Town, SRID: 4326, Encoding: UTF-8
Filed name for Geo-info 2 3 4
Table = Town
Set Correct SRID : 4326
Select .Shp file 1 6
Options
Import 5
Choose Correct Encoding

46. How to check the imported data
Right Click
View Data
View Top 100 Rows

47. Loading Shape Files using shp2pgsql command
Works for Ubuntu/MAC OS X
It is a Command-Line Tool, called shp2pgsql, it will transform shape files to SQL command.
in MAC and ubuntu, please launch "Terminal" again, and execute following command.

48. -s: specify SRID of shape file.
> shp2pgsql -s g geom -W "UTF-8" -c {path_to_.dbf_file} public.Town | pbcopy
-s: specify SRID of shape file.
-g: specify the name of the field for storing geometric object
-W: text encoding of shape file
-c : for creating Table
{path_to_.dbf_file} : specify the path to the .dbf file
public.Town: the name of the table for storing the data of shape file
> shp2pgsql -s g geom -W "UTF-8" -c {path_to_.dbf_file} public.Town | xclip -sel clip
In ubuntu, you have to install xclip first.

49. The easiest way to get "path to .dbf file" :
1. use "Finder" (in MAC) or "file" (in ubuntu), locate and select .dbf file,
2. Right click and select Copy "{filename}.dbf"
3. Go back to terminal, and execute "paste"
Example:
> shp2pgsql -s g geom -W "UTF-8" -c Documents\02Dataset\D1\Town.dbf public.Town | pbcopy
The SQL commands will be sent to System Clipboard.
We then can directly paste into SQL Command window.

50. Execute SQL command to load shape file
Paste into SQL command window, and then execute.
Click

51. How to check the imported data
Right Click
View Data
View Top 100 Rows

52. Practice1 : Import Datasets D1-D3
Please import D2 and D3 with same method to your database.Some details:
For D1: Table: Town, SRID: 4326, Encoding: UTF-8
For D2: Table: MRTLines, SRID: 4326, Encoding: Big5
For D3: Table: MRTStaions, SRID: 3826, Encoding: UTF-8

53. About DataSet D1 Boundary of 368 Taiwanese Towns (shape file)
Table Fields:
Field Name
Data Type
Example Value
Notes
gid
integer 1
Unique ID
townid
character varying (8)
V02
towncode
character varying (12)
countyname
臺東縣
Name of country
townname
成功鎮
Name of town
towneng
character varying (39)
Chenggong Township
countyid
character varying (3) V
countycode
10014
geom
geometry
Geometry object
(MultiPolygon)

54. About DataSet D2 MRT Lines (shape file) Table Fields: Field Name
Data Type
Example Value
Notes
gid
integer 1
Unique ID
mrtid
character varying (9)
mrtsys
character varying (20)
台北捷運系統
Taipei or Kashung
mrtcode
板南線
Name of MRT Line
mrtplan
character varying (1) N
Still in plan?
updatedate
character varying (6)
161117
geom
geometry
Geometry object
(Line)

55. About DataSet D3 Location of MRT Stations (shape file) Table Fields:
Field Name
Data Type
Example Value
Notes
gid
integer 1
Unique ID
landmarkid
character varying (13)
landmarkco
306
landmarkna
character varying (74)
捷運南岡山站-出口1
Name of MRT Station
landmarkad
character varying (7)
address
character varying (77)
高雄市岡山區大…
Address
tel
character varying (35)
updatedate
character varying (6)
161117
geom
geometry
Geometry object
(Point)

56. If you didn't get success with D1-D3
We have something here to help you.
In SVS_0615/Backup subfolder, you shall see: D1.tar, D2.tar and D3.tar.
You can use them to restore a copy from my database.
Use Restore and select the tar file to restore. (see next page)

57. Restore Tables Format Custom or Tar Right Click Filename
Path of Tar File
Rolename
postgres
Restore
Restore

58. Display your Data in QGIS
Layer
Add Layer
Add PostGIS Layer
Next Slider
New

59. Setup Connection from QGIS to PostGIS
Name:
localPostGIS_TBT
(Anything you like)
Host:
localhost
Database:
TaiwanBuddhistTemples V
Username:
postgres V
Password:
Password of postgres OK

60. Connection to PostGIS
Connect
Select Town
Add

61. Quick way to add following PostGIS Laysers
Brower Panel

62. Using Browser Panel
Refresh
Right Click
Add Selected Layer

63. Loading EXCEL like data -- General
Import D4.Population.xlsx
Producre:
S1. Create an empty table in TaiwanBuddhistTemples Database, with 4 fields (tid, city, town, population)
S2. Save .xlsx file to CSV files
S3. Use CSV import utility to import the CSV data

64. S1-1 pgAdmin3 – Create Table
Databases
> TaiwanBuddhistTemples
> Schemas
> Public
> Tables (right click)
> New Table
Next Slider
New Table

65. S1-2 Create Table -- Assign Table Name
Next Slider
Name:
Population
Columns
Owner:
postgres
Click Columns Table for the next step.

66. S1-3 Define Columns Adding city field, as the instruction in next page2
Name:
tid
Data Type:
Integer 3 1 OK
Add

67. S1-3 Character Varying (5)
Continue Adding other fields, as the instruction in next page 2
Name:
city
Data Type:
Character varying
LENGTH: 5 1 3
Add OK

68. S1-4 Define Columns II Next Slider integer character varying (5)
Click Constraints Table for the next step.
Next Slider
Constraints
tid
integer
city
character varying (5)
town
character varying (5)
male
integer
female
integer
popultaion
integer

69. S1-5 Set Primary Key of the Population Tables3
Constraints
Columns 5b 6b 4
tid 5
Add 6 OK 1 2
Primary Key
Add 7 OK

70. CSV (comma spereated )(*.CSV)
S2-1 Save xslx to the CSV
Save Excel files to CSV file.
It should be simple, but it isn't.
The problem is: the CSV file saved by MS EXCEL is only in "BIG-5" encoding, which is not acceptable by postgreSQL CSV import function.
CSV (comma spereated )(*.CSV)

71. S2-2.1 Workaround 1. Save to UTF-8 CSV
Solution1: Use other softwares to open excel files and save to "unicode" encoded CSV files. Ex: LiberOffice or Numbers (MAC)
Running Export function in Page
Select CSV and UTF-8 encoding

72. S2-2.2 Workaround 1. Save to UTF-8 CSV
With LibreOffice
Unicode (UTF-8)
Text CSV OK
Running Savs-as CSV in LiberOffice
Select UTF-8 encoding

73. S2-2.3 Workaround 2. Convert Big-5 CSV to Unicode CSV
Using EXCEL to save .xslx into Big5 CSV, and then we transform it to UTF-8 CSV.
CSV (comma spereated )(*.CSV)

74. S2-2.4 Workaround 2. Convert Big-5 CSV to Unicode CSV
In Windows, open the big-5 CSV with notepad.exe, and save as "utf-8"
Encoding:UTF-8
In MAC, use incov command to transform encoding
> iconv -f BIG-5 -t UTF-8 {path_to_Big-5_CSV} > {path_of_UTF-8_CSV}

75. S2-3 Import CSV with postgresSQL CSV importer
Right Click
Filename
Select the CSV file
Format
CSV
Encoding
UTF-8
Misc Options.
Header v
Delimter
, (comma)
import
import

77. Practice2 : Import Datasets D4 and D5
Please import D5 with same method to your database. details:
For D5: TableName Temples:
Field
type
NULL
Primary Key? id
char varying (7)
NOT NULL
Yes
name
char varying(25)
trait
postcode
integer
longitude
real
latitude
address
char varying(50)

78. Transforms longitude and latitude values in "Temples" to Geo-objects
Add a new column "geom" for Geo-object
Use SQL command to generate Geo-objects and save it to "geom" fields
Columns
Right Click
Add a new field:
Field
type
geom
public.geometry
Properties
Add

79. Run SQL command to create the Geo-object
Execute following SQL command to create Geometric objects from latitude, longitude values.
Click
UPDATE "Temples"
SET geom = ST_GeomFromText('POINT(' || longitude || ' ' || latitude || ')',4326);
UPDATE 5114 Query returned successfully in 1 secs.

80. If you didn't get success with D4,D5
We have something here to help you.
In SVS_0615/Backup folder, you shall see: D4.tar, D5.tar
You can use them to restore a copy from my database.
If the unsuccessful table exists, drop it.
Use Restore and select the tar file to restore. (see next page)

81. Practices:
Try to import your field work data to postGIS, and visualize them in Q-GIS. (Export CSV from Google DOCs)
TableName: Fieldwork
Field
type
Primary Key?
site-id
character(4)
Yes
team
Integer
site-id-team
date-of-collection
date
name-zh
char varying(20)
name-py
char varying(50)
latitude
real
longitude
foundation-date
integer
address
char varying(100)

82. Part4. Simple SQL

83. Simple SQL SELECT postgis_full_version();
SQL, or “Structured Query Language”, is a means of asking questions of, and updating data in, relational databases.
The first SQL in this workshop:
SELECT postgis_full_version();

84. Use SQL to ask questions of the data
Select "TaiwanBuddhistTemples" Database, click "SQL Icon" to start entering SQL command.
Click
Selected
Let Try
SELECT * FROM "Population"

85. Basic SQL syntax (I)
Case 1: Retrieve data from one Table
Select [Field_A, Field_B, Field_C…, *] From TableName
* in fieldname means: all fields
Example:
Retrieving data from Population table, but only city, town and population fields.
Select city, town, population
From "Population"

86. Practice 1:
What is the SQL command for retrieving data from Temples table, but only displaying name, trait, address fields.
Select name, ………….. , …………..
From "……………………."

87. Basic SQL syntax (II)
Case 2: Retrieve data from one Table with conditions
Select [Field_A, Field_B, Field_C…, *] From TableName Where conditions
Condition works a filter, only the records matches the conditions will be returned.
The most common form of conditions is :
Field_X = 'ValueA' ex: city= "New York"
Field_Y < NumberA ex: population < 10000
Field_Z >= NumberB ex: male >= 2000

88. Select countyname, townname From "Town" Where countyname = '新北市'
Example:
“What are the name of the towns in 新北市?”
Select countyname, townname
From "Town"
Where countyname = '新北市'
Practice 2:
“What are the name and population of towns in 臺中市?”
Table name 使用 Double Quote
String 用 Single Quote
Select city, town , …………..
From "Population"
Where city = '…………….'

89. Select ……………. , ………….., trait From "Temples" Where ………………… = '…………….'
Practice 2:
“What are the name and address of templates that are categorized as 道場"
Select ……………. , ………….., trait
From "Temples"
Where ………………… = '…………….'

90. multiple conditions in WHERE clause
You can have multiple conditions in where clause but must you use and/or to combine conditions.
Example:
“lists templates located in '台中市' (postcode: )
Select *
From "Temples"
Where postcode >= and postcode <= 40999

91. Select town, population From "………………."
Practice 3:
“What are the name of temples that are categorized as 道場/道廟/精舍"
Select name, trait
From "Temples"
Where trait = '道場' or trait = '道廟'
or trait = '精舍'
“What are the name of towns that have more than in "新北市"?
Select town, population
From "………………."
Where ……. = …….. and ………. >=

92. Aggregate Function in SQL
In SQL, an aggregation function is a function where the values of multiple rows are grouped together as input to form a single value of more significant meaning.
Sum(column) : Sum all Non Null values over the column
Count(column) : Return number of Non Null values of the column
Avg(column): Sum(column) / Count(column)
Min(column): Minimum value in the column
Max(column): Minimum value in the column

93. Select avg(population) From "Population" Where city='臺北市'
Example:
“The average population of the towns in 臺北市"
Select avg(population)
From "Population"
Where city='臺北市'
How many temples are located in 台北市? (postcode: )
Select count(*)
From "…………………"
Where postcode >= ……… and …….. <= …….

94. "GROUP BY" statement in SQL
The GROUP BY statement is often used with aggregate functions (COUNT, MAX, MIN, SUM, AVG) to group the result-set by one or more columns.
Example:
“What are total population in each city?"
Select city, sum(population)
From "Population"
Group by city

95. Select countryname, count(…………) From "Town" Group by …..
Practice 4:
List number of towns in each city(country)
Select countryname, count(…………)
From "Town"
Group by …..
List ratio of male to total population of each city
Select city, 1.0*sum(…..)/sum(….)
From "Population"
Group by city

96. SQL Joins: connect two or more Tables
A JOIN clause is used to combine rows from two or more tables, based on a related column between them.
Populations
town
population's tid = town's gid

97. SQL Join statement (I)
Case 3: Retrieve data from two or more connected Table
Select [field_A, field_B, field_C…, *] From table1 join table2 on table1.fieldA = table2.fieldB
town
Populations
From "Population" join "Town"
On "Population".tid = "Town".gid
tid
city
town …
gid
countyname
townname

98. List all fieldvalues of connected "Population" and "Town" Table
Example:
List all fieldvalues of connected "Population" and "Town" Table
Select *
From "Population" join "Town"
On "Population".tid = "Town".gid
Example:
List population and geometric information of of top 40 biggest towns ( in terms of population )
select countyname, townname, population, geom
from "town" join "Population"
on "town".gid = "Population".tid
Order by "Population".population DESC
Limit 40

99. Display SQL results in Q-GIS
For showing SQL result in Q-GIS, we need to transform SQL command into a "View".
In SQL, a view is a virtual table based on the result- set of an SQL statement.
You can add SELECT, WHERE, and JOIN statements to a view and present the data as if the data were coming from one single table.

100. Create a View [Townpopulation_top40]
It is very easy to create a view from a SQL command.
Syntax:
CREATE or REPLACE VIEW "name"
AS query
Example:
CREATE or or REPLACE VIEW "Townpopulation_top40" As
select countyname, townname, population, geom
from "town" join "Population"
on "town".gid = "Population".tid
Order by "Population".population DESC
Limit 40

101. Using Browser Panel
Refresh
TownPopulationTop40
Right Click
Add Layer

102. TownPopulation view
Now to create a new view "TownPoulation" for getting the population and boundary of all 368 towns in Taiwan.
Please visualize the "TownPopulation" view in QGIS
Create or REPLACE View "TownPopulation" as
select gid, countyname, townname, male, female, population, geom
from "Town" join "Population"
on "Town".gid = "Population".tid

103. Showing Statistical information in QGIS with "Graduated Style"
In "TownPoulation", we have the population of all 368 towns in Taiwan.
We can use "Graduated Style" function to fill the color of towns according to their populations.
Right Click
Properties

104. Style Graduated 123 population
Use population field to decide the fill-in color
YlOrRd
Or Any color you like
Equal Interval
Separate the range of the possible value of "population" in to 5 "equal interval" classes 5
Classify OK

105. Different Mode of Separating Values
Please Try with different Modes and different number of classes.
Quantile (Equal Count) : Classes will have same number of members
Natural Breaks: Jenks natural breaks classification method, this method seeks to reduce the variance within classes and maximize the variance between classes.
Standard Deviation: it calculates the difference between the filed value of the record in question and the mean value divided by standard deviation of the field value.
("field_name" - mean_value) / standard_daviation

106. Adding Diagram to visualize field values
use "Graduated Style", we can categorize SQL results in to different classes, and fill with different colors.
With "Diagram" function, we can have addition pie-charts or histograms for visualizing field values.
It is especially useful for comparing different values of the same record.

107. PieChart
Size
male
female
Diagrams
Next Slider

108. Size
123 population
Find 10 5
The size of this chart will be proportional to the value of field "population"
Maximal Size will be 10
Minimal Size will be 5

109. Please Try with Histogram

110. Geometry and Spatial Relations
Part5.
Geometry and Spatial Relations

111. PostGIS Geography Type
PostGIS supports following Geography data types:
Simple Geometry
POINT
LINESTRING
POLYGON
Collections:
MULTIPOINT: a collection of points
MULTILINESTRING: a collection of linestrings
MULTIPOLYGON: a collection of polygons
GEOMETRYCOLLECTION: a heterogeneous collection of any geometry (including other collections)

112. Check general information about Geography data types
The following threes functions can be used to retrieve some basic background information of a Geography data field:
ST_GeometryType(geometry) returns the type of the geometry
ST_NDims(geometry) returns the number of dimensions of the geometry
ST_SRID(geometry) returns the spatial reference identifier number of the geometry

113. SQL for retrieving basic geographic information
ST_GeometryType(geometry) returns the type of the geometry
ST_NDims(geometry) returns the number of dimensions of the geometry
ST_SRID(geometry) returns the spatial reference identifier number of the geometry
Example:
List geographic information for "geom" field in town table
Select ST_GeometryType(geom),
ST_NDims(geom), ST_SRID(geom)
From "Town"
Please try with MRTStations, MRTLines, Temples

114. Functions for Point Functions only for Point data type:
ST_X(geometry) returns the X ordinate
ST_Y(geometry) returns the Y ordinate
ST_AsText(geometry) Returns the Well-Known Text (WKT) representation of the geometry/geography without SRID metadata.

115. SQL for retrieving basic geographic information of Point/MultiPoint type
ST_X(geometry) returns the X ordinate
ST_Y(geometry) returns the Y ordinate
ST_AsText(geometry): Returns the Well-Known Text (WKT) representation of the geometry/geography without SRID metadata.
Example:
List geographic information for "geom" field in MRTStations table
Select ST_X(geom), ST_Y(geom), ST_AsText(geom)
From "Temples"
Please try with MRTStations

116. Functions for LineString
Functions only for LineString :
ST_Length(geometry) returns the length of the linestring
ST_StartPoint(geometry) returns the first coordinate as a point
ST_EndPoint(geometry) returns the last coordinate as a point
ST_NPoints(geometry) returns the number of coordinates in the linestring

117. SQL for retrieving basic geographic information of LineString type
ST_Length(geometry) returns the length of the linestring
ST_StartPoint(geometry) returns the first coordinate as a point
ST_EndPoint(geometry) returns the last coordinate as a point
ST_NPoints(geometry) returns the number of coordinates in the linestring
Example:
List geographic information for "geom" field in MRTLines table
Select ST_Length(geom), ST_NPoints(geom),
ST_StartPoint(ST_GeometryN(geom, 1)),
ST_EndPoint(ST_GeometryN(geom, 1))
From "MRTLines"
ST_GeometryN(geom, 1) : Get the 1st geometry object from a collection

118. More About ST_Length The SRID of MRTLines Table is : 4326 (WGS84)
The default unit of measuring length of geometry object with SRID 4236 is "degree"
In order to get result in "meters", we need to transform the object back to general geography type:
Select ST_Length(ST_Transform(geom,4326)::geography)
From "MRTLines"
ST_Transform(geom,4326)::geography : transform geom field from SRID:4326 to geography type

119. Select ………(ST_Length(ST_Transform(geom,4326)::geography))
Practice 5:
“How long is MRT 板南線"
Select ………(ST_Length(ST_Transform(geom,4326)::geography))
From "MRTLines"
Where …… = '板南線'
"List the name and total length of each MRT Lines"
Select mrtcode, ………(ST_Length(ST_Transform(geom,4326)::geography))
From "MRTLines"
Group by ……..

120. Functions for Polygon Functions only for Point/MultiPoint data type:
ST_Area(geometry) returns the area of the polygons
ST_NRings(geometry) returns the number of rings (usually 1, more of there are holes or islands)
Select townname,
ST_Area(ST_Transform(geom,4326)::geography) as area,
ST_Nrings(geom)
From "Town"
Order by area DESC

121. From town join population on town.gid=population.tid
Practice 6:
“List total area (in km2 ) of all counties in Taiwan"
Select …, …..(ST_Area(ST_Transform(geom,4326)::geography))
From "Town"
Group by ….
"List the Population density (persons/ km2)of all towns in 新北市"
Select …, …..../
From town join population
on town.gid=population.tid

122. Your Exercises
Please try to fill colors to the 10 biggest town in Taiwan( in terms of area).

123. Use of Spatial Relationships
Spatial databases have the ability to compare relationships between geometries.
Questions like “Which are the closest MRT Staions to a temple?” or “How many people are live in the towns which has a least one MRT line going through." This can only be answered by comparing geometries representing the MRT stations , MRT lines, and towns.

124. ST_Intersects
ST_Intersects(geometry A, geometry B) returns t (TRUE) if the two shapes have any space in common, i.e., if their boundaries or interiors intersect.

125. ST_Intersects Examples
Example: List towns which intersects with "金山區"
(1) The geometry object of "金山區"
select geom from "Town" where countyname='新北市' and townname='金山區'
(2) Select records from Town table, where record's geom has intersects with geometry object of "金山區"
Select townname, geom
From "Town"
Where ST_Intersects(geom, **) //** is geometry object of "金山區"
(3) Combine those two Quries.
See. next page

126. Try to visualize them in QGIS
select geom from "Town" where countyname='新北市' and townname='金山區' +
Select countyname, townname, geom
From "Town"
Where ST_Intersects(geom, **) //** is geometry object of "金山區" =
Select countyname, townname, geom
From "Town"
Where ST_Intersects(geom, (select geom from "Town" where countyname='新 北市' and townname='金山區' ) )
Try to visualize them in QGIS

127. ST_Crosses
ST_Crosses(geometry A, geometry B) returns TRUE if their intersection "spatially cross", that is, the geometries have some, but not all interior points in common.
The intersection of the interiors of must have a dimensionality less than the maximum dimension of the two input geometries.

128. ST_Cross Examples Select * From "MRTLines" Where ST_Crosses(geom, (
Example: List MRT Lines which crosses "新北市 板橋區"
(1) The geometry object of "新北市 板橋區"
select geom from "Town" where countyname='新北市' and townname='板橋區'
(2) Select records from MRTLines table, where record's geom cross with geometry object of "金山區"
Select *
From "MRTLines"
Where ST_Crosses(geom, (
select geom from "Town" where countyname='新北市' and townname='板橋區' ) )
One limitation, the above query works only if the subquery returns exactly one record !!
So, this method cannot answer the question from other prospect:
List all Towns which is crossed by MRT Lines "板南線"

129. ST_Cross Examples II Select countyname, townname, "Town".geom
Example: List all Towns which is crossed by MRT Lines "板南線"
We perform spatial join to solve the problem
Select countyname, townname, "Town".geom
From "Town" join "MRTLines"
on ST_Crosses("Town".geom, "MRTLines".geom)
where mrtcode='板南線'

130. Practice :
List MRT Lines which crosses the Town where more than person lives
Select "MRTLines".gid,mrtcode, "MRTLines".geom, "Town".townname
From "Town" join "MRTLines"
on ST_Crosses("Town".geom, "MRTLines".geom)
join "Population" on "Town".gid="Population".tid
where Population >
order by "Town".townname

131. ST_Within and ST_Contains
ST_Within and ST_Contains test whether one geometry is fully within the other.

132. Example: List all Temples in "金山區" and "萬里區"
Select "Temples".id,"Temples".name, "Town".gid,"Town".townname
From "Temples" join "Town"
on ST_Within("Temples".geom, "Town".geom)
where "Town".townname='金山區' or "Town".townname = '萬里區'
Practice:
List the number of Temples in every town in '台中市'

133. ST_Distance and ST_DWithin
An extremely common GIS question is “find all the stuff within distance X of this other stuff”.
The ST_Distance(geometry A, geometry B) calculates the shortest distance between two geometries and returns it as a float.
the ST_DWithin(geometry A, geometry B, distance) function provides an index-accelerated true/false test. This is useful for questions like “how many trees are within a 500 meter buffer of the road?”.

134. Example:
List all Temples located within 500 meters of "善導寺站"
Select "Temples".id, "Temples".name,"MRTStations".landmarkna,
ST_Distance(
ST_Transform("Temples".geom,4326)::geography,
ST_Transform("MRTStations".geom,4326)::geography )
from "Temples" join "MRTStations"
on ST_DWithin(
ST_Transform("MRTStations".geom,4326)::geography,
500)
where "MRTStations".landmarkna='捷運善導寺站'

135. Practice:
what is the nearest MRTStations (or exist) to the temple "金龍禪寺(d114A20)"
Hint: 1. use last example as template
2. if you want to join two tables without any field in common, use "cross join" instead of "join"