GIS on the Web; web sources of GIS data

1
GIS on the Webweb sources of GIS data
2
Web Mapping Defined
Web servers and map viewer clients interact to -

• Discover, access and retrieve views from
  multiple servers

• Display multiple layers of geographic data
  within a single web application

• Query and update

• Provide interface for visualization, Decision
  Support, etc.

• Support geocoded raster, vector, matrix, and
  other data

3
Mapping on the Web Today
How can I combine data from each of these sources
to answer my question?
4
Metadata

• Needed to automate the process of search for data
• compare using a library catalog
• Needed to determine the fitness of a data set for
  use
• particularly regarding quality
• Needed to handle data effectively
• e.g., format
• Needed to identify notable data contents
• e.g., to find images of an interesting hurricane

5
Metadata can be Expensive to Generate

• They represent a high level of abstraction
• and may need an expert to define
• But the benefits are substantial
• metadata make it possible to find data sets, and
  use them effectively
• they allow the benefits of investments in data to
  be realized

6
The U.S. FGDC Standard

• Content Standards for Digital Geospatial Metadata
  (CSDGM)
• Defined by a committee of U.S. Federal agencies
• Now widely used worldwide
• The basis of a new international standard
• Potentially several hundred items for one data
  set
• but easily boiled down to a much smaller number

7
The Dublin Core Standard

• Devised by the digital library community
• Suitable for any type of data, geospatial
  included
• easily extended to include essential items for
  geospatial data
• e.g., the latitude and longitude limits of the
  data sets coverage

8
Demo Websites

• http//webclient.alexandria.ucsb.edu/
• http//geodata.gov/

9
Data Portals
10
Online
11
The data portal
12
Service consumers
Excel
Web browser
Fortran/C/VB/Java codes
portal
User registration/authentication/authorization (9)
Application services analysis, mapping,
charting, models,
workflow, integration (8)
R
ArcGIS
Conversion
Certificate
Server
Server
engine
authority
Data registration/Search/ Query rewriting
orchestration.(6)
Ontology source and
services (7)
DL services layer
(5)
External data resources registry
DL metadata
Resource drivers (2)
Digital Library
STORET
NAWQA
. . .
Core grid services monitoring nodes, scheduling,
data transfer, replication, collection
management,(1)
Sensors
Sensors
Sensors
Sensors
PoP Node
PoP Node
PoP Node
PoP Node
13
USGS National Mapping
14
US GeoDataftp access toDEMDLGGNISGIRASetc.
15
NOAA Weather and other data
16
Why build an SDI?

• Build data once and use it many times for many
  applications
• Integrate distributed providers of data
  Cooperative governance
• Place-based management
• Share costs of data creation and maintenance
• Support sustainable economic, social, and
  environmental development

17
Types of geospatial standards

• Data Classification
• e.g., Vegetation Classification
• Data Content
• e.g., Digital Geospatial Metadata, Spatial
  Schema
• Data Symbology or Presentation
• e.g., Digital Geologic Map Symbolization
• Data Transfer
• Data Services (Web Mapping, Feature)
• Data Usability
• e.g., Geospatial Positioning Accuracy

18
What is the OpenGIS?

• Open Geospatial Consortium (OGC)
• Non-profit, international voluntary consensus
  standards organization
• Industry, government, and university members
• Over 260 members worldwide 30 countries 5
  continents
• 91 European members - 19 countries
• 35 Asia-Pacific members - Japan, Republic of
  Korea, Australia, China, and Thailand
• OGC collaborates and works closely with
• International Organization for Standardization
  (ISO)
• World Wide Web Consortium (W3C)
• OASIS
• And others

19
Approved Specifications

• Simple Feature Access OLE, SQL, CORBA
• Catalog 1.1.1
• Coordinate Transformation 1.1
• Grid Coverages 1.0
• Web Map Service 1.1.1 (2.0 in final edit) (WMS)
• Geography Markup Language 3.0 (GML)
  529 pages alone!!!
• Web Feature Service 1.0
• Filter 1.0
• Style Layer Descriptor 1.0 (SLD)
• Web Coverage Service 0.0 (WCS)
• OpenLS
• OGC Web Services (Ongoing)
• Web Map Client Configuration

20
WMS Web Map Service

• Mature, well-established specification
• Version 1.0 issued 2000-04
• Version 1.1.1 issued 2001-12
• Server client support in many vendor products
  freeware
• Scope geographic data rendered as images
  ("maps"),not actual data values
• Similar to ArcIMS Image Server

Demo Returns an Image Cubewerx
http//demo.cubewerx.com/demo/cubexplor/cubexplor.
cgi?
21
GEOSPATIAL Acronym Soup

• WMS Web Mapping Service (image)
• WFS Web Feature Service (vector)
• WCS Web Coverage Service (raster)
• GML Geography Markup Language (XML)
• ArcXML ESRI XML language for Map Services
  (being depreciated)

22
OGC Web Map Service Interfaces

• GetCapabilites
• GetMap
• GetFeatureInfo

23
WMS - getCapabilties

• allows the server to advertise what it can do
• available layers
• supported output projections
• supported output formats
• scale hints
• extent of data
• XML format

24
WMS - getMap

• allows the retrieval of a map from a web server
• user supplies bounding box, image size, format,
  error handling, etc
• server responds with an image, typically a
  web-ready format like GIF, PNG or TIFF

25
GetMap Request Example

• http//b-maps.com/map.cgi?VERSION1.1.0
• REQUESTGetMap
• SRSEPSG4326
• BBOX-97.105,24.913,78.794,36.358
• WIDTH560
• HEIGHT350
• LAYERSBUILTUPA,COASTL,POLBNDL
• STYLES0XFF8080,0X101040,BLACK
• FORMATimage/png
• BGCOLOR0xFFFFFF
• TRANSPARENTTRUE

26
WMS getFeatureInfo

• allows the retrieval of simple feature attributes
• user supplies an x,y coordinate pair and a layer
  of interest
• server responds with attribute information in
  HTML, GML or arbitrary ASCII format
• optional interface

27
WMS Limitations

• all you get is a picture, not the data
• limited control over how the data is styled
• particularly limiting with regards to labeling
• supports only a small portion of functionality
  typically supported by a vendor

28
Style Layer Descriptor enabled Web Map Service

• In a basic WMS style is just a name that
  identifies a specific layer portrayal
• An SLD WMS adds the ability to control layer
  style
• An SLD WMS adds the following additional
  operations that are not available on a basic WMS
• DescribeLayer
• GetLegendGraphic
• GetStyles
• PutStyles
• These interfaces are described in the SLD
  specification document

29
WFS Web Feature Service

• WFS 1.0 approved 2002
• ISO has requested it be submitted
• Scope storage retrieval of geographicvector
  feature data (point/line/polygon)
• Hydrography, Transportation, Government Units,
  Cadastral, Geodetic Control
• Similar to ArcIMS Feature Server

30
OGC Web Feature Server Interfaces

• OGC WFS Interfaces
• GetCapabilites
• DescribeFeatureType
• GetFeature
• Transaction
• LockFeature/GetFeatureWithLock
• Response to GetFeature request is formatted using
  GML (typically)

31
Two classes of WFS
Basic WFS A basic WFS would implement the
GetCapabilities, DescribeFeatureType and
GetFeature operations. This would be considered a
READ-ONLY web feature service. Transaction WFS A
transaction web feature service would support all
the operations of a basic web feature service and
in addition it would implement the Transaction
operation. Optionally, a transaction WFS could
implement the LockFeature operation.
32
Basic WFS

• GetCapabilities
• A web feature service must be able to describe
  its capabilities. Specifically, it must indicate
  which feature types it can service and what
  operations are supported on each feature type.
• DescribeFeatureType
• A web feature service must be able, upon request,
  to describe the structure of any feature type it
  can service.
• GetFeature
• A web feature service must be able to service a
  request to retrieve feature instances..

33
Transaction WFS
Transaction A web feature service may be able to
service transaction requests. A transaction
request is composed of operations that modify
features that is create, update, and delete
operations on geographic features. LockFeature/Get
FeatureWithLock A web feature service may be able
to process a lock request on one or more
instances of a feature type for the duration of a
transaction.
34
DescribeFeatureType

• Generates a schema definition for the requested
  features using the language specified in the
  capabilities document (XML schema is mandatory,
  others are optional)
• The XML schema document must be a valid GML
  application schema and defines the schema of the
  feature types listed in the request.
• Feature geometry must be expressed using the GML
  geometry description.
• Spatial Reference Systems must be consistent with
  GML

35
GetFeature

• The GetFeature operation allows retrieval of
  features from a web feature service.
• The request contains queries which may
  unconstrained or constrained by a Filter
• Filter is described in described in the Filter
  Encoding Specification
• The output format is GML by default but the
  specification allows other formats

36
Basics of GML

• Geography Markup Language (GML) is an XML grammar
  written in XML Schema for the modeling,
  transport, and storage of geographic information.
• GML provides a variety of kinds of objects for
  describing geography including features,
  coordinate reference systems, geometry, topology,
  time, units of measure and generalized values.
• GML includes
• Geometries and Coordinate Reference System (based
  on EPSG)
• A temporal reference system (based on ISO 8601)
• A Units of Measure (UOM) dictionary

37
GML 3.0

• GML models various resources required to describe
  geospatial information
• Features (including coverages and observations).
• Coordinate Reference Systems
• Units of Measure
• Values (as values of feature properties)
• Topology and Geometry (as values of feature
  properties)
• Temporal (as values of feature properties)

38
The Three Architecture Cases
The Graphic Element Case
The Data Case
The Picture Case
(source OpenGIS document 99-077)
39
Architectures for Different Applications

• Each map request sends new geometry
• Examples find by address or another attribute
  routing, single-attribute maps, weather maps,
  etc.
• In general situations when geometry is defined
  by attribute (categorical coverages, for example)
• Geometry remains relatively constant
• Examples atlases, statistical maps for
  collection zones (states, counties, census
  tracts)
• In general situations with many attributes for
  limited number of geometries
• For the latter case makes sense to cache and
  re-use coordinate information on the client side
  as much as possible. For each application, there
  is some right mix of the two approaches.

40
From Geography Markup to Rendering
lt?xml version"1.0" encoding"iso-8859-1"?gt ltrsgt lt
rgtltnamegtHorton Plazalt/namegtltURLgtlt/URLgtltlabelposgt41
.46,77.51lt/labelposgtltcgt5076,1540 4986,1540
4895,1539 4803,1539 4715,1539 4622,1539 4534,1538
4534,1641 4534,1745 4534,1856 4622,1856 4711,1856
4800,1856 4893,1855 4984,1855 5075,1854 5075,1749
5076,1646 lt/cgtlt/rgt ltrgtltnamegtGaslamplt/namegtltURLgtlt/U
RLgtltlabelposgt44.60,83.00lt/labelposgtltcgt5162,1013
5084,1057 5083,1116 5081,1222 5079,1326 5079,1433
5076,1540 5076,1646 5075,1749 5075,1854 5167,1854
5257,1855 5257,1750 5259,1647 5260,1541 5262,1434
5262,1328 5263,1222 5263,1013 lt/cgtlt/rgt . . .
XML encoding of geographic features (such as GML)
41
ltsvg id"axiomap" onload"initMap(evt)"
onmousemove"GetElementAndPosition(evt)"
onmousedown"set_menu()" . . . gt ltrect
id"canvas" fill"white" stroke-width"0" x"0"
y"0" width"100" height"100"/gt
ltdescgtlt/descgt ltdefsgt ltmenu id"MENU"
xmlns"http//foo"gt ltheadergtCustom
Menult/headergt . . . lt/menugt lt/defsgt   ltg
id"map" style"stroke-linejoinround
stroke-linecapround"gt ltg id"background_poly
gons"/gt ltg id"base_thematic"/gt ltg
id"foreground_polygons "/gt ltg
id"optional_polygons "/gt ltg id"foreground_line
s"/gt ltg id"optional_lines"/gt ltg
id"foreground_points"/gt ltg id"optional_points"
/gt ltg id"cosmetic"/gt   ltg id"tooltips"
style"shape-renderingoptimizeSpeed"gt . .
. lt/ggt   ltg id"stable_gui_elements
style"shape-renderingoptimizeSpeed"gt ltg
id"map_title" style"visibilityvisible"gt .
. . lt/ggt ltg id"layer_navigation_group"gt
. . . lt/ggt ltg id"legend" style"visibilityhi
dden" . . .gt . . . lt/ggt . . . lt/ggt
lt/ggt ltg id"extras"gtlt/ggt lt/svggt
42
Geography Network

• The Geography Network is a global community of
  data providers who are committed to making
  geographic content available.
• This content is published from many sites around
  the world, providing you immediate access to
  the latestmaps, data, and related services.

43
Geography network

• View Live Maps      
• Download Geodata
• Build Custom Applications     
• Publish Your Content
• Find Useful Tools     
• Share Your Ideas

44
Geography Network and ArcIMS Lab
45
Accessing Geography Network

• Overlaying recent earthquakes on population
  information
• Start ArcMap, New empty map
• File-add data
• GIS Severs, select Geography Network services
• Add ESRI_pop, ESRI_Quake_rec__fs
• Zoom into a region (floating tools pallet has
  zoom tool)
• Change the symbology for the ESRI_Quake_Rec_FS
• Right click on a layer, select properties, go to
  the Symbology tab.
• Click template. Change the color.
• Export Recent Quakes
• Right click on Earthquakes (Last Month),
• DatagtExport Data
• Add data to the map
• Change the symbology
• Rick Click properties, Select Symbology tab in
  dialog
• Click quantities graduated symbols, ValueMag.
• Click Classify, and see the distribution of the
  data

46
What Happening behind the scenes

• ArcMap sends a request to the ESRI servers for an
  image from the ESRI_Pop server for a region
• Server responds. ArcMap draws map
• ArcMap asks for a feature set from the
  ESRI_Quake_Rec_FS server.
• ArcMap receives records, draws maps