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1. DATA COLLECTION AND INPUT OVERVIEW
• The process of getting the data into computer is called as data
encoding in GIS.
• The process of data encoding and editing is often called as Data
Stream.
• The first step in creating a database in GIS is to acquire the data and place
them in the system.
• GIS must be able to accept wide range of datasets.
• Often user generates his own datasets in GIS.

2. • There are number of methods for inputting the data into GIS.
• Obtaining data is an important part in GIS.
• GIS data is obtained from various sources, however they are classified
into 2 types.
• – Primary data sources
• – Secondary data sources

3. • Primary data – Data measured directly by surveys, field data
collection, remote sensing
• Secondary data – Data obtained from existing maps, tables or other
data sources
• Primary data We cannot usually observe the spatial distribution of a
variable throughout the study area
• Therefore we need to take measurements of a subset of the features
in the area that best captures the actual spatial variation
• Sampling of primary data
• The sampling density determines the resolution of the data
• Samples taken at 1 km intervals will miss variation smaller than 1 km
• Standard approaches to sampling:
 – Random
 – Systematic
 – Stratified
• Random samples • Every location is equally likely to be chosen

4.  Systematic samples • sample points are spaced at regular intervals
 Stratified samples • Requires knowledge about distinct, spatially
defined sub-populations
• More sample points are chosen in areas where higher variability is
expected
Secondary data(existing datasets)
• More and more ready-made digital GIS data sets become available
• Government agencies:
• census geography
• Topographic surveys
• Private companies

5. • Meta-data: “data about the data”
– Procedures used to collect or compile the data
– Data lineage
– Accuracy and measurement standards
– Coding schemes
Required for both spatial and attribute data
• Meta-data often absent
This leads to
– Misinterpretation
– Misuse
– False perception of accuracy

6. Data sources
• The existing datasets in the analogue or digital form needs to be
encoded and should be compatible with GIS.
• There are different types of data sets available in the real world and
they exist in different formats.
• Hence, we should use different methods for encoding and editing the
datasets to make them compatible with GIS for extracting the
information.
• Not always data is directly available, in many situations we have to
create the datasets ourselves.
• Some times data becomes obsolete, there also we will create new
data for an area.
• The data created will be in many forms like in the form of drawings,
photographs, survey statistics, survey data etc.

8. DATA INPUT METHODS
Before discussing data input techniques, its important to know various
types of data.
– Analogue (non-digital) spatial data
– Digital spatial data
• Analogue data are normally in paper form and include paper maps,
tables of statistics and hardcopy aerial photographs.
• All these forms of data need to be converted to digital form before
use in a GIS.
• Digital data like remote sensing data are already in compute-readable
formats and are supplied on diskette, magnetic tape or CD- ROM or
across a computer network.

9. DATA INPUT METHODS
• There are four methods of data input which are widely used:
– keyboard entry
– manual digitising
– automatic digitisation
– Scanning
Other than the above mentioned methods of files are directly transferred
into GIS which is called direct file translation.
Keyboard Entry Method
• This method is also called as key coding.
• It is the entry of data into file for GIS at a computer terminal.
• This technique is used for attribute data that are available only on paper.
• This technique can be mixed with digitising process for the creation of GIS
database

10. • The attribute data, 'once in digital format, are linked to the relevant
map features in the spatial database using identification codes.
• There are unique codes that are allocated to each point, line and area
feature in the dataset.
• The coordinates of spatial entities like point, line and area features can
be encoded by keyboard entry.
• – However, it will not be convenient when the number of features are
more.

11. • This method leads to obtain very high level of precision data by entering the
actual surveying measurements.
– Used for entering land information during digitization
– Can be used for drawing maps using survey measurements
Manual Digitising
• Manual digitising is the most common method of encoding spatial features
from paper maps.
• It is a process of converting the spatial features on a map into a digital format.
• Point, line, and area features that form a map, are converted into (x, y)
coordinates.
• A point is represented by a single coordinate, a line by a string of coordinates,
and, when one or more lines are combined with a label point inside an outline,
then an area (polygon) is identified.
• Hence, digitizing is called as the process of capturing a series of points and
lines.

12. Procedure- Manual digitizing
 The map is affixed to a digitising table.
 Three or more control points are to be identified and digitised for each map
sheet – Ex:- intersection of roads, historic monuments etc.
 The points are called reference points or tics or control points.
 The coordinates of these points are known to the person who is doing
digitizing.
 The coordinates of these points are used by the system to perform necessary
mathematical operations and also to calculate coordinates of remaining
features present in the map.

13. Problems with digitizing the map
• The accuracy of the output of the digitisation depends upon the experience
and skill of the operator and density of points, lines and polygons of the map.
• Accuracy also depends upon the selection and distribution of the control
points.
• Some of the common problems in digitizing paper maps are:
 Paper maps are unstable; each time the map is removed from the digitising
table, the reference points must be re-entered when the map is affixed to the
table again.
 If the map has stretched or shrunk in the interim, the newly digitised points
will be slightly off in their location
 Errors occur on these maps, and these errors are entered into the GIS data
base as well.
 The level of error in the GIS database is directly related to the error level of the
source maps
 Maps are meant to display information, and do not always accurately record
vocational information

14. • While performing digitization there is possibility of errors
– Positional errors
– Overshoots
– Undershoots
– Spikes
– Etc.
• Hence, proper care should be taken while digitizing a map so that all required
features will be present and no feature will be missing.
• Scanning and Automatic Digitising
• Scanning is the most commonly used method of automatic digitising.
• This method is normally used when raster type of data is to be produced from
analogue maps.
• And the scanned image can be used as the base for digitizing the features in
vector format.
• Different types of scanners are used for scanning the maps.
• – Flatbed scanners
• – Rotating drum scanners

15. COGO Method
• COGO full form is – Coordinate Geometry method
• It is a methodology for capturing and representing geographic data
• This method uses survey measures for plotting the data in CAD/GIS
systems.
• Survey measurements like bearings and distance are used in this
method for plotting the features

16. • Coordinate Geometry (COGO) is a method of inputting surveying or
engineering data into GIS, CAD or mapping software's.
• These data may be collected in the field using conventional surveying
techniques and instrumentation, or may be derived from existing maps, plats,
engineering plans, drawings or records.
• Data collected in the field consist typically of coordinates of points, distances
and bearings between points, and point identifiers (with possibly additional
descriptions for these points).

17. • The data are observed and recorded through standard field surveying
procedures, such as a traverse or a series of layout measurements.
• The data may be non-digital (recorded in notebooks), or digital
(recorded on some sort of total station or data logging device)
• In the latter case the data will be transferred to office computers
through specialized software.
• Existing maps and plans include subdivision plans, showing legal lot
boundaries, and engineering drawings.
• In both cases features are depicted with some coordinate values, and
distances and bearings or offset distances are shown between the
features.