Hotspot Analysis with GeoMedia Grid Shaun Falconer

What is hot spot analysis?

• A method of detecting and presenting

patterns in data

• Common approaches

– Point map

– Thematic map

– Density estimation map

Density

Clusters

Patterns

Concentrations

Sparse input

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

• Input: (Vector) point dataset of incidents

• Output: Density map

Hotspot Detection

• Input: Density map

• Output: Hotspot map

Vectorize hotspots

• 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

• 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

The volume of the kernel shapes

needs to be equal

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

Results: Fixed bandwidth vs Adaptive bandwidth

Discrete Hotspot (The Process)

Mean := Multiple of Mean

Classification > Hotspot Detection Interpolation > Density

X

Y

Y X

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?