Hotspot Analysis with GeoMedia Grid
Shaun Falconer
What is hot spot analysis?
• A method of detecting and presenting
patterns in data
Sparse input
Density
• Common approaches
– Point map
– Thematic map
– Density estimation map
Patterns
Clusters
Concentrations
Point Map
Thematic Map
Hotspots from Density map
Density (Hotspot) Maps
• We are looking at point source density
hotspot
Alternative presentation of density: Isolines
Some examples
• Crime event analysis
• Asset or utility analysis
e.g. outage location analysis
e.g. repair analysis
• Epidemiological events
(pandemic locations)
• Transportation events
e.g. accident location analysis
• Earthquake events
e.g. hotspot of earthquake by magnitude
• Bore hole samples by Magnesium level
GeoMedia Grid provides hotspot analysis
• GeoMedia Grid processes grid data using
statistical and probability functions
• Provides functions targeted directly at point
based hotspot analysis
– Local scan interpolation over sparse point data
to produce density isopleth map – bit like a
DEM map
– Tools to process the density map, such as
•
•
•
•
Hotspot extraction
Isolines (like contours from DEM)
Thematic of density map
Input to further analysis, either grid or vector based
Where does Grid fit in with GeoMedia?
• GeoMedia is vector
• GeoMedia Grid is raster (cell, grid)
• They are integrated
- Preliminary analysis typically undertaken in
GeoMedia.
E.g. source of data, aggregate or merge data,
filter data, generate functional attributes
- Rasterise to grid and identify hotspots
- Within GeoMedia GWS environment and display
- Vectorize the hotspots for further analysis,
display or storage
A quick walk through …
High level process
Density
Command
Hotspot
Detection
Vectorize
hotspots
• Input: (Vector) point dataset of incidents
• Output: Density map
• Input: Density map
• Output: Hotspot map
• Input: Hotspot map
• Output: Vector dataset of hotspots
Density Command
1. Use GeoMedia to identify Point dataset
2. Grid> Define New (study area)
– Define extents of area of interest
– Resolution (say 30m)
3. Grid> Interpolation> Density
– Select
• Point source identified in step 1.
• If available in dataset, set the Intensity
– Rest are pre-populated defaults
Density Command
• Density map will be shown in GeoMedia
Input to Density Command
(Optional) Thematic of Density Map
• Grid> Layer> View Legend
– Set precision: right click
legend> Format
• Click ‘Value’ then click ‘Format’
• Enter Decimal value (data
dependent, e.g. 6), OK
– Set colour sequence: select all
entries (use shift)
• Right click, colour sequence
• Choose start to end colours
• Choose path type
– Apply
Result: Thematic Density Map
Hotspot Detection
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•
•
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Grid> Classification> Hotspot Detection
Source: Density Map from previous step
Multiple of Mean: data dependent. Try 5
OK
Result: Hotspot of density map
Finally: Vectorize hotspot map
• Grid> Layer> Vectorize to Feature
• Layer name: Hotspot output from previous
step
• Conversion type: Area
• Output type: Partitioned Boundary
• Check ‘Simplify output’
• Confirm output feature
class name
Result: Feature class that can be used in GeoMedia
• E.g. extract incidents within the hotspot for
closer examination
Some theory …
Adaptive bandwidth, kernel shapes and density
Point B has neighbors closer to it than Point A, so the adaptive
bandwidth for Point A is larger than that for Point B, since the
adaptive bandwidth takes the average distance of the (in this
case, 5) nearest neighbors of each point
The volume of the kernel shapes
needs to be equal
Results: Fixed bandwidth vs Adaptive bandwidth
Discrete Hotspot (The Process)
Interpolation > Density
Classification > Hotspot Detection
X
Y
X
Y
Mean := Multiple of Mean
Where does GeoMedia Incident Analyst fit in?
• GeoMedia Incident Analyst is an extension
that uses GeoMedia and GeoMedia Grid
principally targeted at crime analysis
workflows, that incorporates hotspot
analysis in the workflow.
3D hotspot maps
• Thematic 3D maps further augments
understanding of spatial phenomena
• GeoMedia Grid with GeoMedia 3D can be
used to create 3D hotspot maps
• 3D thematic maps allow map readers to
understand relationships within seemingly
unconnected/unrelated data
• Webinar was held on 10 September – look
for recording shortly at
http://geospatial.intergraph.com/Resources/
webinars/ArchivedWebinars.aspx
Questions?