1. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Geocoding & GPS

2. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Summary Introduction to Geocoding Geocoding: Concepts and Definitions Relationship to other Census Processes Approaches to Data Collection NSO Benefits & Concluding Remarks Introduction to GPS How GPS Works Sources of Error & Accuracy Selecting a GPS Advantages & Disadvantages

3. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Introduction Many NSOs have a specialized coding scheme and understand geocoding as a dynamic process Clarification within the statistical community Expansion and discussion on components and methods within the process of geocoding

4. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Geocoding: Concepts and Definitions Definitions: Conceptual Operational Geocoding vs Georeferencing

5. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Geocoding can be broadly defined as the assignment of a code to a geographic location. Usually however, Geocoding refers to a more specific assignment of geographic coordinates (latitude,Longitude) to an individual address. The purpose of this section is to introduce geocoding concepts relevant for census mapping and the different approaches to related data collection. Reference: UN Report of the Expert Group Meeting on Contemporary Practices in Census Mapping and Use of Geographical Information Systems (2007)

6. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Definition of Geocoding Conceptual - 2 situations: The more general process of assigning geographic codes to features in a digital database. A GIS function that determines a point location based on an address. It could generally be expected that such point locations will be relatively precise (eg + /-2m) in accuracy and will be based upon use of GPS technology. Operational Geocoding is the computer oriented process which converts information about a unit from which statistical information is collected into a set of coordinates describing the geographic position of that unit

7. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Definition of Geocoding (cont.) Operational Elements Collecting precise data at the level of point locations (or very low geographic level such as a city block) and assigning codes for use in dissemination. Coding the centroid, building corners, or building point of entry coordinates for a unit such as a block of land, building or dwelling Coordinates must contain latitude and longitude or standardized x and y points for gridded interpolation. A Z or Zed coordinate may represent altitude or elevation Codes cover each geographic unit and have a combinational relationship to distinguish different units (Enumeration Areas/Blocks)

8. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Geocoding vs. Georeferencing Geocoding A GIS operation for converting street addresses into spatial data that can be displayed as features on a map Georeferencing Aligning geographic data to a known coordinate system so it can be analyzed, viewed, and queried with other geographic data

9. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Relationship to Other Census Processes N.S.O Senior Managers must evaluate when the use of geocoding should be considered and consideration must be given due to: - range of hardware and software - availability of resources (street network reference layers, address database) - staff skill set - funding - user demands

10. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Relationship to Other Census Processes (cont.) Movement into a fully GIS based approach to census mapping Generation of high quality maps for use in the collection phase Reduction of work required for updating maps for future censuses Aggregation of records into customized units for satisfying users’ requirements

11. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Census Enumeration & the Geocoding System Delineation irrespective of the existence of address Ability to apply a geocode to any geographic areal unit Flexible Coding Scheme Ability to incorporate future administrative divisions Pre-enumeration geocoding critical links between GIS boundaries and tabular census data

12. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Census Hierarchies Internal political Boundaries Areal unit aggregation Resolution suitable to NSO needs and user demands Considers available datasets for continuous development The smaller area defined by the geocode the more flexible the results for subsequent users

13. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Blocks Enumeration Areas Country District Province Locality Given Country BuildingDwelling Census Hierarchies

14. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Geocoding Classifications Disaggregation into Spatial Entities or Civil Divisions and Compatibility 1 st RegionProvince 2 nd DistrictMunicipality 3 rd Town/Village 4 th Dwelling Resultant geocoded units placed within a set of Latitude and Longitudinal boundaries

15. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Geocoding Classifications (cont.) Initial creation of Civil Divisions through digitizing or segmentation/pixel based-approaches Low to Zero levels of sampling through the accurate placing of coded units, but flexible enough to include changes Appropriate detail that fits with the boundaries of a geographic area for a given country

16. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Coding Scheme

17. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Data Collection Methods Two main methods: Direct Collection Approach Matching Approach

18. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Direct Collection Approach Digitizing from available topographic maps Direct collection using field techniques (ex.GPS) Areas, Street, Dwelling Global Positioning System (GPS)Digitizing from a topographic map

19. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Matching approach Using an Address locator database and street network database in a GIS Joining an address database to an existing spatial database for the area of interest First Avenue Second Avenue Right of Street Left of Street #1#99 #2#100 address number Main Street First Avenue Right of Street Left of Street #1#99 #2#100 #51 #32 Nodes Second Avenue Street Segment Street Network

20. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Data Maintenance Cleaning AddressesCleaning Addresses Retaining only the key address elementsRetaining only the key address elements Establish a Matchcode (indicator of which address elements will determine the geocode)Establish a Matchcode (indicator of which address elements will determine the geocode) Eliminating extraneous charactersEliminating extraneous characters Standardizing SpellingStandardizing Spelling

21. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Staff Expertise Recommendations Task/conditionDirect collectionMatching Existence of digital base map for countryHighly desirable Statistical staff with expertise in use of GPSEssentialNot Essential Acquisition of large numbers of GPS receiversEssentialNot Essential Geo-referenced list of addresses or equivalentNot EssentialEssential Excellent address matching algorithmsNot EssentialEssential Existence of a rational, consistent, and locally- recognized addressing system for housing units Highly desirableEssential

22. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Geocoding: Benefits for NSO’s Improved map creation for the field Customizable map outputs for specified regional activities Coding techniques are transparent and transferable Fixates the groundwork for future statistical activities and coding schemes

23. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Concluding Remarks Technologies are accessible and allow delineation irrespective of the existence of address There is a need for an agreement on a definition of geocoding for census purposes Many available methods and technologies exist to support accurate geocoding frameworks Geocoding system is value-added for GIS based Spatial Analysis of Statistical Data

24. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Global Positioning Systems (GPS) Technology has revolutionized field mapping in recent years Prices of GPS receivers have dropped GPS methods have been integrated in many applications User groups are widespread (utilities management, surveying and navigation) GPS has contributed and advanced to improve field research in areas such as biology, forestry,geology, epidemiology and population studies GPS has become a major tool in census cartographic applications

25. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Global Positioning Systems (cont.) Preparation and updating of enumerator (EA) maps for census activities Location of point features such as service facilities or village centers Coordinates can be downloaded or entered manually into a digital mapping system or GIS, and can be combined with existing, georeferenced information

26. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 How GPS Works GPS receivers collect the signals transmitted from more than 24 satellites—21 active satellites and three spares. The system is called NAVSTAR, and is maintained by the U.S. Department of Defense The satellites are circling the earth in six orbital planes at an altitude of approximately 20,000 km. At any given time five to eight GPS satellites are within the “field of view” of a user on the earth’s surface The position on the earth’s surface is determined by measuring the distance from several satellites

27. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 The global positioning system (GPS)

28. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 The global positioning system (cont.) GPS satellites circle the Earth twice a day … The satellite signal: Three kinds of coded information essential for determining a position; The receiver: 1. Calculates the distance to the first satellite user is able to catch. 2. Calculates the distance to a second satellite for which it is able to catch a signal. 3. Repeats the operation mentioned under point 2 with a third satellite.

29. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 c b a How GPS determines a location’s coordinates

30. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Sources of GPS signal errors Good visibility and bad visibility of satellites due to obstacles signal multipath Uncontrollable sources of error over which the user does not have control Atmosphere delays Receiver clock errors Orbital errors

31. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 GPS Accuracy Inexpensive GPS receivers Within 15 to 100 meters for civilian applications. Differential GPS reduces error further Accuracy of about 3-10m can be achieved with quite affordable hardware and shorter observation times. More expensive systems and longer data collection for each coordinate reading can yield sub-meter accuracy.

32. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Problems with GPS In dense urban settings, the possible error of standard GPS (standard ~15m up to 100 meters) may not be sufficient Differential GPS can be used for cross-checking GPS readings with other data sources published maps aerial photographs sketch maps produced during fieldwork

33. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Differential GPS

34. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Selecting a GPS Unit Commercially available GPS receivers vary in price and capabilities Technical specifications determine the accuracy by which positions can be achieved The more powerful a receiver, the more expensive it will be In many mapping applications, the accuracy of standard systems is quite sufficient Receivers also vary in terms of user-friendliness, tracking capabilities which are useful in navigation

35. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Summary: Advantages and Disadvantages of GPS Advantages Fairly inexpensive, easy-to-use field data collection Modern units require very little training for proper use Collected data can be read directly into GIS databases minimizing intermediate data entry or data conversion steps Worldwide availability Sufficient accuracy for many census mapping applications—high accuracy achievable with differential correction

36. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Summary: Advantages and Disadvantages of GPS Disadvantages Signal may be obstructed in dense urban or wooded areas Standard GPS accuracy may require differential techniques Differential GPS is more expensive, requires more time in field data collection and more complex post-processing to obtain more accurate information A very large number of GPS units may be required for only a short period of data collection.

37. Workshop on International Standards, Contemporary Technologies and Regional Cooperation, Noumea, New Caledonia, 04–08 February 2008 Where’s your Datum