The practice of representing data with geospatial information can be observed in many disciplines and in our everyday life too. Use of free solutions is very popular and usually making the first steps easy. However, what happens if the amount of data exceeds a critical value, and we will face bad visual experiences or the performance of the system dramatically decrease because of the large number of features? Advanced IT skills can help to overcome this issue, but without them, browsing the reference guides and textbooks will not probably help, and we will give up. Presented by Marianna Zichar, assistant professor, University of Debrecen

2. • Keyhole Markup Language
• Range of potential users
• NetworkLink
• Region
• NetworkLink & Region
• Existing solutions
• My classification
• Conclusions
Overview
5th GIS Conference 29 May – 31 May 2014, Debrecen

3. • XML based language to describe
features with geospatial information
• Google Earth / Map
• Generable by the application, but
editable
• Simple text file with kml (or kmz)
extension
• OpenGIS KML 2.2 Encoding Standard
Keyhole Markup Language
5th GIS Conference 29 May – 31 May 2014, Debrecen

4. • Abstract elements with derived
elements
• Inheritance from ancestors
• gx: Google extension
namespace
Class tree for KML elements
5th GIS Conference 29 May – 31 May 2014, Debrecen

5. Geometry
5th GIS Conference 29 May – 31 May 2014, Debrecen

6. • Geographers
• Surveyors
• Medical researchers, physicians
• Epidemiologists
• Biologists
• Linguists
• Agronomists
• Architects
• Catastrophe managers
• Retailers
• Etc.
Range of potential users – motivation
5th GIS Conference 29 May – 31 May 2014, Debrecen

7. • Use the GUI of GE and save your features
• Limited customization
• Not all the KML elements are available
The most simple way to create

8. • Hundreds of placemarks
• Large files
• Decreasing performance
• Editing is hard
• Solution
• Divide and conquer
• Network link & Region
Issues
5th GIS Conference 29 May – 31 May 2014, Debrecen

9. • Simple element referencing another KML file or KMZ archive
• The fetched KML file can contain
• A hierarchy of Feature elements
• One (optional) <NetworkLinkControl> element that controls the
behaviour of the source (fetching) KML file.
• A hierarchy of network linked KML files can be created.
NetworkLink
5th GIS Conference 29 May – 31 May 2014, Debrecen

10. • For complex sets of KML files, you can partition the KML into
multiple files that link to each other.
• When data is changing frequently, the interval refresh feature of
<NetworkLink> provides for timely refresh of the displayed data.
• When data is distributed over a large area of the Earth’s surface,
view-based refresh feature enables GE to perform a spatial
search based on the current viewpoint and load only the data
that is currently within the user’s view.
• For very large data sets, the region feature allows you to control
which parts of the data set are shown in a given view.
Why to use Network Links?
5th GIS Conference 29 May – 31 May 2014, Debrecen

11. • Refers to a geographical area of 2D or 3D which extension is specified by
its bounding 2D or 3D box.
• Can be assigned to any KML feature
• The features of a region are visible if the region itself is visible on the
screen and it can be contained by a box with an edge length falling
between two values specified as minLodPixels and maxLodPixels.
Region
5th GIS Conference 29 May – 31 May 2014, Debrecen

12. • The networklink element
has a viewRefreshMode
subelement, which value
has to be set onRegion to
fetch the referenced file
content according to the
active status of the
region.
NetworkLink with Region
5th GIS Conference 29 May – 31 May 2014, Debrecen

13. • No tool in GE interface to define regions 
• Regionator
• Free Python library to divide thousands of placemarks,
polygons and paths into separate regions for better
viewing.
• Requires programming skills.
Existing solutions
5th GIS Conference 29 May – 31 May 2014, Debrecen

14. • KML2KML
• Commercial application with a number of tools for
reorganizing and optimizing KML files.
• Creates one single region to each checked feature types
based on their minimal bounding boxes
• No possibility to divide the features of the same type to
several regions with different LOD values.
Existing solutions
5th GIS Conference 29 May – 31 May 2014, Debrecen

15. • Further commercial applications (e.g. Arc2Earth) do
exist.
• Some companies offer services of creating data in
KML format as well.
• In spite of these opportunities, my personal
experiences show that a practical guide is needed.
Existing solutions
5th GIS Conference 29 May – 31 May 2014, Debrecen

16. The objectives of the most frequent usage methods
related to placemarks are:
• To reduce the number of placemarks
packed closely together.
• To separate different types of data
into layers.
• To fade features in and out of view.
Objectives
5th GIS Conference 29 May – 31 May 2014, Debrecen

17. Regions with the same bounding box are used but with different
LOD settings and the goal is to increase the number of visible
features from the same area while zooming in.
Features have to be grouped into several folders assigning the
same bounding box to each of them.
Case 1.
5th GIS Conference 29 May – 31 May 2014, Debrecen

18. • Increase the performance of rendering when the number
of the futures is critical, but the aggregation level is
acceptable .
• Features have to be divided into separate files.
• The main KML file contains references to the files with the
help of network links. Every network link has an associated
region, where the LOD can be even the same, but the
bounding box match the physical extent of the features.
• Computer does not have to manage data in memory,
which are actually not visible, then the performance of our
system will definitely grow.
Case 2.
5th GIS Conference 29 May – 31 May 2014, Debrecen

19. • If the spatial distribution of the placemarks is
approximately consistent then a classical quadtree
structure is perfect to represent the nested regions.
Case 3.
5th GIS Conference 29 May – 31 May 2014, Debrecen

20. I provided some practical guidelines by differentiating
three cases, where instructions and explanations help
the users without strong IT skills to manage large
amount of data.
Conclusions
5th GIS Conference 29 May – 31 May 2014, Debrecen

21. Thank you for your attention.
5th GIS Conference 29 May – 31 May 2014, Debrecen