GIS for Disaster Risk Management

Introduction To GIS

Pau Aragó Galindo

parago@uji.es

September 2012

 

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This work is licensed under a
Creative Commons Attribution-ShareAlike 3.0 Unported License.

 

What are you going to learn in this chapter

 

 

1 Introduction

1.1 Why spatial is special?

2 Spatial Data Model

2.1 Raster Model

2.2 Vector Model

3 GIS database

4 Spatial reference system

5 Bibliography cited and recommended

 

1 Introduction

What do GIS means?.GIS has a lot of meanings, but the main two are Geographic Information System and Geographic Information Science or geospatial science. The first terminology has been use by the industry which are providing the software, the second terminology is often more use by academy world. Nevertheless the important issue is that GIS is a junction of software data and people working with spatial data.

 

Thinking about GIS it is like a big box were we can put a lot of things, such as GPS, maps, cartography, on-line maps and so on. All the things that we can found in this big box have something in common, SPATIAL. Next video will show an overview of the possibilities geospatial technologies.

 

http://www.youtube.com/watch?v=poMGRbfgp38&feature=youtube_gdata_player

 

The video you have seen show how geospatial technologies are changing the way we move get and manipulate spatial information. Nowadays it is possible to search information in Internet using a map or see the results of a search represented in a map, some searches shows results related with our actual place without user even notice that. We will use Internet as a source for our data and a place to share our results. This course is focus in the GIS as Geographical Information System as union of hardware, software, spatial data and people.

 

Hardware

 

The hardware is the machine with all its components were the software is running.  Hardware requirements depend on how complex is the analysis we will perform, the number of data records we will manage, visualization techniques we are going to implement,... Nowadays almost every PCU is capable to run a GIS software for a basic data processing

 

Software

 

There is a lot of alternatives. This link shows you an overview of it, http://en.wikipedia.org/wiki/Comparison_of_geographic_information_systems_software. There are proprietary and non proprietary software, depending on software's license. Table 1  shows a list of advantages and disadvantages of both alternatives.

 

 

 

Proprietary software

Free and open source software

Advantages

  • Warranty1 of developing company on product (holds for every company)

  • Components should work together

  • Usually well documented software

  • No license fees

  • Unrestricted use (e.g., no limits for the number of installations)

  • No update enforcement

  • Support of open standards

  • Support usually available from several providers2

  • Customization at API level and below

Disadvantages

  • Software price and maintenance fees

  • Training costs

  • Maintenance tied to specific licensed companies

  • Customized development can be difficult due to available resources of vendors

  • Support only as long as software company exists

  • Installation know‐how necessary3

  • Training costs4

Table 1: Advantatges and disadvantatges propietary an non propietary software.1BUT: license agreements often exclude warranty.2On FOS GIS support see: http://www.osgeo.org/search_profile.3BUT: most FOS desktop GIS provide installers (e.g., for MS‐Windows a setup.exe).4BUT: user's choice to invest in own resources or to buy external services. Source: (Steiniger i Bocher 2009)

GIS technologies and advances in GIS visualization are responsible of a great variability of maps visualizations that today can be realized. In this web, http://owni.eu/2011/12/09/the-best-maps-of-2011/, you have an example of some maps done in 2011 to represent spatial data. Nevertheless, it is necessary to point out that behind dose maps there is a lot of work on data collection, analysis, manipulation and visualization techniques. In conclusion, GIS is not data visualization or creation of a map. GIS is more than that, it is data collection, share data, data analysis, share results and may be finally make a map

1.1 Why spatial is special?

Spatial information is important because “almost everything that happens, happens somewhere. Knowing where something happens could be critically important(Longley et al. 2011). This sentence is important fore disaster risk management to know which areas could be vulnerable to plan prevention and response. For instance, One of the first use of maps to do an spatial analysis was done by John Snow during cholera outbreak in London (year 1854). John Snow used a map of London streets to study cholera individual cases distribution. The map point to the source of the decease, a water pump (see  Fig. 1). “A picture tells a 1000 words”

 

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Fig. 1. A variant of the original map drawn by Dr. John Snow (1813-1858), a British physician who is one of the founders of medical epidemiology, showing cases of cholera in the London epidemics of 1854, clustered around the locations of water pumps.

Mandatory lectures

 

What is a GIS. http://volusia.org/gis/whatsgis.htm

 

Exercises

 

Write a document with the answer and deliver it to your teacher using the class folder. Also, answer the questions in the Class Forum

 

  1. Read GIS definitions from this link. http://www.colorado.edu/geography/gcraft/notes/intro/intro_f.html . Are you agree with this definitions? Which one do you prefer?

  2. Write 5 example of data that will improve its meaning when it is spatially represented. Find an example of these data spatially represented in Internet

  3. Find an example in which the use of GIS will be useful for risk disaster management. Explain why.

 

Recommended lectures

 

Goodchild, Michael F. 2010. “Twenty Years of Progress: GIScience in 2010.” Journal of Spatial Information Science (1) (July). doi:10.5311/JOSIS.2010.1.2. http://josis.org/index.php/josis/article/view/32.

 

 

Online Resources;

Video. Introduction to GIS. http://www.youtube.com/watch?v=7g3GUYlYfZM&feature=related

Open Source Geospatial Foundation. http://www.osgeo.org/

2 Spatial Data Model

Spatial data links alphanumeric information with a specific location. Alphanumeric information is displayed in a computer screen according on object's location. This is call data model, “it is a set of construct for describing and representing selected aspects of a real world in the computer” (Longley et al. 2011). GIS basic Data Models are Vector Model and Raster Model. Spatial information is displayed in a GIS using layers of spatial information. A layer could be base on a raster or vector data model

2.1 Raster Model

Raster Model is based on cell grid call pixel as representation of the real world.  This model is like the digital pictures we are very familiar. A digital picture or image has millions of pixels, each pixel displays one color an all the pixels altogether displays the image captured with the camera, see Fig. 2. Raster model use in GIS works exactly in the same way.

 

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Fig 2. This example shows an image with a portion greatly enlarged, in which the individual pixels are rendered as little squares and can easily be seen. Source, http://en.wikipedia.org/wiki/File:Pixel-example.png

Representing real world with this data model is very simple. A raster image stores a numerical value per pixel. Raster data model is use mainly to represent continues features such as temperature, elevation or aerial and satellite images. Fig 3 shows different features representation using a raster data model.

 

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Fig 3: Landscae representation using a raster model. Source http://courses.washington.edu/gis250/lessons/introduction_gis/images/grid_data_model_0.gif

 

Basic raster image metadata information we could get within raster files use with a GIS are :

 

Raster images manipulation is done mainly using mathematical equations, algebraic algorithms, masks or reclassifying raster images values. If we are merging different raster images, usually, it is mandatory that the images had the same pixel size and extension. The output result when we us as input more than one raster image will be as accurate as the worst image accuracy.

 

Principally GIS software only can store one value per pixel. Nevertheless, as an example Miramon1 software can associate to raster layer an alphanumeric table. Use of this alphanumeric table will potentially increase raster image analysis possibilities.

 

Table 2 shows a list of raster file formats supported by gvSIG software:

Source

Type

Name

Read

Write

Notes

File

Raster

ecw

Yes

No

 

File

Raster

sid

Yes

No

 

File

Raster

img

Yes

Yes

Erdas

File

Raster

gif

Yes

No

 

File

Raster

tiff

Yes

Yes

 

File

Raster

jpeg

Yes

Yes

 

File

Raster

jp2

Yes

Yes

 

File

Raster

png

Yes

Yes

 

File

Raster

asc

Yes

No

 

File

Raster

raw

Yes

No

 

File

Raster

ppm

Yes

Yes

PNM files in RGB

File

Raster

mpl

Yes

Yes

Ilwis

File

Raster

bmp

Yes

Yes

 

File

Raster

dat

Yes

No

Envi

File

Raster

lan

Yes

No

Erdas

File

Raster

gis

Yes

No

Erdas

File

Raster

pix

Yes

No

PCI Geomatics

File

Raster

aux

Yes

No

PCI Geomatics

File

Raster

adf

Yes

No

ESRI Grids

File

Raster

rst

Yes

No

IDRISIS

File

Raster

kap

Yes

No

 

File

Raster

ers

Yes

No

 

File

Raster

pgm

Yes

No

PNM files in grey scale

File

Raster

rmf

Yes

No

Raster Matrix Format

Table 2: Raster formats suported by GvSIG. Source: http://www.gvsig.org/web/projects/gvsig-desktop/devel/gvsig/1-10-0/formats/

Mandatory Lecture

Raster data model.   http://geodata.ethz.ch/geovite/tutorials/L2GeodataStructuresAndDataModels/en/html/unit_u2Raster.html

2.2 Vector Model

The vector model is based on point, lines and polygons, see Fig. 4. Visually is very similar to a CAD2 model, but functionally it has an import difference. Vector CAD data model doesn't have a topological relation among layer's features. What is a topology? “Topology is the science and mathematics of relationships used to validate the geometry of vector entities, and for operations such as network tracing and test of polygon adjacency” (Longley et al. 2011). Using topological relations a computer is able to know which feature is at right or left, connected with,... Topology issue is very important for spatial analysis and for GIS in general. Without a topology it is impossible to do a network analysis or a spatial join. Vector data model stores topological relationships internally. Object's position is stored and which objects are connected with and its relative position. If you want to now more about how topology is store in a GIS vector model visit this link.

 

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Fig 4: Vector Data Model, point lines and póligons.

Associated to the graphical information there is a table containing the alphanumerical information. The table stores alphanumerical information related with each of the geographical objects. Each row of the table corresponds to on spatial object (point, line or polygon). Figure 5 shows a polygon layer and its associated table.

 

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Fig 5: Polygon layer and its associated table. Screenshot from gvSIG.

 

Table S'ha produït un error: No s'ha trobat la font de referència shows a list of vector formats supported by GvSIG software:

 

Source

Type

Name

Geom type

Read

Write

Format ver.

Notes

File

Vector

shp

2D

Yes

Yes

 

 

File

Vector

shp

3D

Yes

Yes

 

 

File

Vector

shp

2D-M

 

 

 

 

File

Vector

gml

 

Yes

No

3.1.2 (SFP-2)

 

File

Vector

gml

 

Yes

No

02/01/02

 

File

Vector

kml

 

Yes

No

02/01/12

 

File

Vector

dxf

 

Yes

Yes

 

 

File

Vector

dwg

 

Yes

No

v12

 

File

Vector

dwg

 

Yes

No

v13

 

File

Vector

dwg

 

Yes

No

v14

 

File

Vector

dwg

 

Yes

No

v15

 

File

Vector

dwg

 

Yes

No

2004

 

File

Vector

dgn

 

Yes

No

 

 

DDBB

Vector

PostgreSQL

2D

Yes

Yes

 

 

DDBB

Vector

PostgreSQL

3D

 

 

 

 

DDBB

Vector

PostgreSQL

2D-M

 

 

 

 

DDBB

Vector

MySQL

 

Yes

Yes

 

 

DDBB

Vector

Oracle Spatial/Locator

 

Yes

Yes

9i

Requires manual installation of the Oracle proprietary libraries to work.

DDBB

Alfa

H2

 

Yes

Yes

 

 

DDBB

Vector

H2+HatBox

 

Yes

Yes

 

 

DDBB

Alfa

Generic JDBC

 

Yes

Yes

 

 

DDBB

Vector

ArcSDE

 

 

 

 

Requires manual installation of the ArcSDE proprietary libraries to work.

Table 3: Vector formats suported by GvSIG. Source: http://www.gvsig.org/web/projects/gvsig-desktop/devel/gvsig/1-10-0/formats/

There are formats such as GML or KML that represent point, lines and polygons in the same file. Whereas these formats are useful to interchange data are not recommended to do a productive work. In a productive GIS environment it is recommended to work with file formats that stores point, lines and polygons in different files.

Mandatory Lecture

Vector data model. http://geodata.ethz.ch/geovite/tutorials/L2GeodataStructuresAndDataModels/en/html/unit_u3Vector.html

 

Exercises

 

  1. Go to OSM www.openstreetmap.org. What data model do you think they are using?

  2. Go to Google maps www.maps.google.com. What data model do you think they are using?

3 GIS database

GIS database is similar to other database systems. As we have introduced in the previous section, vector model is always associated with a table which has information about the spatial objects graphically represented. A GIS database is a collection of tables related to each other containing alphanumeric information associated to a spatial object.

A table has a unique identifier for each row. This identifier could be use to join different tables using the unique identifier of both tables to match the rows of the different tables. In this way it is possible to manage spatial information and alphanumeric information coming from different sources and not necessary georeferenced. The only requisite to join two tables is to have a row describing the same attribute and using the same identifier.

If you want to know more about database you have more information in this MIT course link. Yo

4 Spatial reference system

Spatial reference systems (SRS) is a coordinate system, local, regional or global to locate every geographical object on a map. Sometimes you will see coordinates expressed in latitude longitude (Fig 6) and sometime expressed in meters using Universal Transversal Mercator (UTM) projection.  UTM coordinates is the result of spherical world projected to a developable surface such as cylinder (Fig. 2) or cone where the coordinates could be expressed in meters.

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Fig 6: Latitude and longitude of the earth. Source: http://en.wikipedia.org/wiki/File:Latitude_and_Longitude_of_the_Earth.svg

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Fig 7: Mercator projection. Source: http://www.nationalatlas.gov/articles/mapping/a_projections.html

It is important to know that if you overlay two layers from the same place with different SRS, these layers are not going to be properly displayed in the GIS software screen because these layers have not the same SRS. Sometimes positional difference could be from some meters to thousand of meters. Therefor, it is important to know the SRS of each layer you are working on and change the SRS of the layers to a common one.

In this web page you can find all the SRS http://spatialreference.org/

Recomended lectures

http://www.nationalatlas.gov/articles/mapping/a_latlong.html

http://maps.unomaha.edu/Peterson/gis/notes/MapProjCoord.html

http://www.nationalatlas.gov/articles/mapping/a_projections.html

5 Bibliography cited and recommended

 

Longley, Paul, M. F Goodchild, David Maguire, and David W. Rhind. 2011. Geographic information systems & science. third. Hoboken, NJ: Wiley.

Steiniger, Stefan, and Erwan Bocher. 2009. “An Overview on Current Free and Open Source Desktop GIS Developments.” International Journal of Geographical Information Science 23 (10): 1345–1370. doi:10.1080/13658810802634956.

Longley, Paul, M. F Goodchild, David Maguire, i David W. Rhind. 2011. Geographic information systems & science. third. Hoboken, NJ: Wiley.

 

 


1 http://www.creaf.uab.es/miramon/

2 Computer Aided Desing. http://en.wikipedia.org/wiki/Computer-aided_design