1. Extracting or collecting geospatial data
Session 4 –
Making a good map –
Extracting or collecting geospatial data
Sokna Sek – MOH/DPHI
Leng Ing – MOH/DPHI
Sat Chab – MOH/DPHI
Steeve Ebener – HGLC
Izay Pantanilla – HGLC

2. How do you create geographic data?
Extracting or collecting geographic data
How do you create geographic data?
When it comes to the geographic objects:
By using remote sensors placed on a satellite or in a plane (remote sensing)
By processing the images resulting from remote sensing (image processing)
By extracting the geographic coordinates of point type object or the topology of line/polygon objects from 1 or 2 (digitizing)
By collecting the geographic coordinates of places in the field using a GNSS enabled device (Surveying)
The method you will most likely be using

3. How do you create geographic data?
Extracting or collecting geographic data
How do you create geographic data?
When it comes to the geographic objects it is important to remember to comply to the defined dataset specification:
Scale of work
Accuracy and resolution for raster format geospatial data
Accuracy and precision level for vector format geospatial data

4. How do you create geographic data?
Extracting or collecting geographic data
How do you create geographic data?
When it comes to attributes (statistics, information)
By attaching the attribute to its corresponding object, preferably through the use of its unique ID coming from the master list
master list
District ID
Stats/Info
Geocoding: A GIS operation for converting street addresses into spatial data that can be displayed as features on a map, usually by referencing address information from a street segment data layer. (Esri GIS dictionary)

5. How do you create geographic data?
Extracting or collecting geographic data
Extracting or collecting geographic data
How do you create geographic data?
When it comes to attributes (statistics, information)
It is therefore key that any field survey aiming at collecting health related data contains the necessary fields to link with the corresponding master list and its unique IDs!
Exercise 1

6. Extracting or collecting geographic data
Global Navigation Satellite Systems (GNSSs)
Definitions
Global Navigation Satellite System (GNSS): Satellite navigation systems that provide autonomous geo-spatial positioning with global coverage. This include the GPS, GLONASS, Galileo, BeiDou, and other systems.
Geo-spatial positioning: The ability to locate yourself or an object on the surface of the earth. Generally using geographic coordinates expressed in terms of latitude and longitude

7. Extracting or collecting geographic data
GNSSs – GPS vs GLONASS vs BEiDou vs Galileo
All these systems allows to precisely identify locations on Earth

8. Extracting or collecting geographic data
GNSSs – How does it work?
- Identifier
Almanac Data
(status & orbital info to
calculate which satellites
are visible)
Ephemeris Data
(precise orbital info to
calculate satellite location)

9. Extracting or collecting geographic data
GNSSs – How does it work? ?

10. Extracting or collecting geographic data
GNSSs – How does it work? ?

11. Extracting or collecting geographic data
GNSSs – How does it work?
Reason why you need at least 3 satellites signal to get a good reading (4 recommended)

12. Extracting or collecting geographic data
GNSSs – Source of signal errors
Poor PDOP
Good PDOP
PDOP: Positional Dilution of Precision

13. Extracting or collecting geographic data
GNSSs – Source of signal errors
Accuracy: 69 m
Accuracy: 46 m
Accuracy: 44 m
Accuracy: 19 m
Accuracy: 14 m
Accuracy: 12 m
Accuracy: 7 m
Better to have a good dispersion and looking
at the accuracy measure given by the device

14. Extracting or collecting geographic data
GNSSs – Source of signal errors

15. Extracting or collecting geographic data
GNSSs – Source of signal errors 1 2 1 2
Signal Multipath
Take the reading in the most open
space possible

16. Extracting or collecting geographic data
GNSSs – Which device to use
Large choice / different prices!
Minimum requirements:
1. Allows to be set up as follow:
a. Position format: hddd.ddddd
b. Map datum: WGS84
c. Map Spheroid WGS84
d. Distance and speed: Metric
2. Provide a reading with at least 5 digits to reach a level of precision down to the meter
3. Display the following information:
a. Number of received satellite signals
b. Accuracy measure
4. Having access to both the GPS and GLONASS constellations is a plus

17. Extracting or collecting geographic data
GNSSs – Why latitude/longitude (Decimal degrees)?
Most comprehensive and powerful method of georeferencing
Standard, stable, unique, infinitely fine resolution
Uses a well-defined and fixed reference frame
Based on Greenwich (Prime) Meridian and Equator

18. Extracting or collecting geographic data
GNSSs – Scale, accuracy and precision
15 m
Recommended

19. Extracting or collecting geographic data
GNSSs – Unit setting
Match the data specifications
Taking a reading
Coordinates
GPS and GLONASS on
Position of the satellites
Accuracy value
Number of received satellite signals

20. Extracting or collecting geographic data
GNSSs – Different data collection methods
Without GNSS
enabled devices
Uses GNSS
enabled devices

21. Extracting or collecting geographic data
GNSSs – The importance of having a protocol/SOP
Description of the device
How to use the device (buttons, batteries,…)
How to set it up
Step by step process to collect the reading
TRAINING

22. Extracting or collecting geographic data
GNSSs – Checking during data collection
The better the data collection process is the less data cleaning/validating is needed
Importance of defining and applying standards and protocols
Checking for horizontal accuracy
Collect information once - Use it many times !!!

23. Extracting or collecting geographic data
GNSSs – Checking during data collection
Use of Google drive and Google Map
if internet connection is available

24. Extracting or collecting geographic data
GNSSs – Cleaning after data collection
Check and clean
Data collection date
Infrastructure name and code
Administrative division name spelling and code
Geographic coordinates
Painfull process!!
Better to directly collect the data properly

25. Global Navigation Satellite Systems (GNSSs)
GNSSs – When you are done with the device
On site, between data collection points
For longer period of time
Remove the batteries
from the device
Store the device in
A dry place

26. Global Navigation Satellite Systems (GNSSs)
GNSSs – Summary
Choose the appropriate device/method
Set the unit as per the data specifications
Use a pre-established protocol/SOP
Signal lost indoors and reflected off buildings and other near by objects => choose an open space
Takes time to calibrate and get accurate reading – wait 1 minute to finalise coordinates
Minimum 4 satellites
Collect coordinates with 5 digits after the decimal point
Ethics of mapping households and GPS tracking

27. Global Navigation Satellite Systems (GNSSs)
GNSSs – Android device and GPS Essentials
GPS Essentials is a free application available for Android- based devices with a built-in GNSS receiver.
It can be used as an alternative to dedicated GPS devices when collecting geographic coordinates as it complies with the specifications discussed in the previous slides.

28. Global Navigation Satellite Systems (GNSSs)
GNSSs – Android device and GPS Essentials
Separate document
Installation guide for GPS Essentials
SOP to follow and data collection form to use when collecting geographic coordinates using an android phone and GPS Essentials
First exercise of this training
Exercise 1