Geocoding & Data Collection with GPS. 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
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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
The purpose of this section is to introduce geocoding concepts relevant for census mapping and the different approaches to related data collection.
“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.”
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
Define census geographic hierarchy
Develop geographic coding scheme
Development of an administrative and census units listing
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
A small country could use the following coding scheme:
Province 2 digits
District 3 digits
Locality 4 digits
EA 4 digits
An EA code of 10 025 0105 0073 means that enumeration area number 73 is located in province 10, district 25 and locality 105.
The unique code is stored in the database as a long integer or as a 13-character string variable.
Digitizing from a topographic map
Global Positioning System (GPS)
Left of Street
Left of Street
Right of Street
Right of Street
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
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
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 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
Good visibility and bad visibility of satellites due to obstacles
Uncontrollable sources of error over which the user does not have control
Receiver clock errors
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.
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