gis data models: how to georeference a farm?
TRANSCRIPT
GIS data models: how to
georeference a farm?
Nicola Ferrè
The spatial characteristics of an object
..there are many ways to spatially “describe” a farm..
Observer 1 Observer 2
definition
any establishment,
construction or, in the case
of an open-air farm, any
place in which animals are
held, kept or handled
the whole area and all
infrastructures on it under
the control of an operator
to perform agricultural or
aquaculture activities
granularity 1 spatial element >1 spatial element
primitive point polygon
scalablesame shape for whole
scales
multi-scale spatial
represetnation
The spatial characteristics of an object
Definition: In order to be able to represent an object
inside a GIS, we first need to define what
we are referring to.
Granularity: Granularity is a level of details. Granular
objects are those, which are at low level
detail in your GIS
Primitive: A graphic representation of a location
Scalability: Scale affects the degree of generalization
of features being mapped.
The spatial characteristics of an object
..there are many ways to spatially “describe” a farm..
..we need an information model to represent an
object in a GIS software, in order to..
1. capture and precisely state requirements to
represent the object so that all stakeholders may
understand and agree about them,
2. think about the design of the system, process, and
the tool that will be used to capture the information,
3. explore multiple solutions also from the economical
point of view.
The spatial characteristics of an object
What is an information model and why do
you need one?
1.An Information Model provides the framework for
organizing your content so that it can be delivered
and reused
2.The framework assists authors and users in finding
what they need
Once you have created an Information Model for your content
repository, you will be able to label information in ways that will
enhance search and retrieval
Information model
From a geomatics point of view, an information
model allows the user to create a representation
of how an object looks on a GIS software
Definition
Spatial characteristic
Choose the primitive and attributes
Information model
Definition: ..in natural language..
[..] any place in which animals are held, kept or
handled [..]
[..] spatial information on zones where specific
management, restriction or regulative regimes
are established [..]
• establishing a dictionary of the terminology used
• giving some examples (e.g. photos, drawings) to
exemplify the concept
Information model
Spatial characteristic: to consider only
the “essential” spatial elements that
characterize the objecto some element must be ignored (e.g.: silos, farmer house)
o some other identified (e.g.: building, shelters, plots)
..you should choose which is the relevant spatial
characteristic of the object according to your interest.
Remember: features are often "vague, gradual, or fuzzy"
Information model
Information model
Primitive & attribute - accuracy
Accuracy: Detail with which features are
represented (both spatial and properties).
Elements to consider:
• what you intend doing with the feature
• grain and extent (scale)
• costs of capturing and maintaining the
feature
Information model
Primitive & attribute - usage
Typical spatial information usage:
• .. just to produce a simple map of the..
• Object inventory
• Spatial calculation (e.g.: distance, surface)
• Spatial analysis (e.g.: spatial density, hot
spot)
Information model
Primitive & attribute - scale
• Map scale affects map detail ► a larger
scale map can show more detail than a
smaller scale map.
• Information content is correlated with
grain and extent
Grain: is the size of the individual units of observation;
i.e., the finest unit of management
Extent: is the spatial domain over which the system is
studied and for which data are available
Information model
Primitive & attribute
Generalisation vs Abstraction
• Generalisation: Generalization is the
method used in GIS to reduce detail in
data (by removing details, a geographic
feature become simplified)
• Abstraction: A simplified idea of a real-
world object
Information model
Primitive & attribute
Generalisation vs Abstraction
With the abstraction process we simultaneously
focus on important characteristics of
geographic content, structure, and process
while temporarily suppressing certain details,
rather than on the elimination or deletion of
details (generalisation).
Information model
Primitive & attribute - costs
• As scale gets larger, accuracy gets
better, and cost increases
Decide on a map accuracy that meets your
requirements and that you can afford
Take home message # 1
Before to start to collect geospatial data you need to
define (clearly) an information model
Take home message # 2
An information model is based on:
Take home message # 3
Scale, cost, and accuracy are inseparably intertwined
Content accuracy: imprecise definition
Spatial accuracy: incoherent spatial representation
Attribute accuracy: wrong proprieties
Take home message # 4
Abstraction and generalization are fundamental to
define the way to represent an object
..consider ALWAYS the costs for data production and
management..
Information model
Questions?
Information model – practical example
Goal: to georeference the farms of an
area in Italy to produce a farm
distribution map
Step 1: Definition
I do not need to provide a farm definition that is
suitable for every circumstance inside and outside the
veterinary domain, I need a definition that is
specifically thought for the spatial element
of farms and for the identified goal
Information model – practical example
farm: an area organised by an operator
to perform activities related to
animal keeping
To improve the consensus of this definition I can refer
to legislation, or scientific publications
Information model – practical example
farm: an area organised by an operator
to perform activities related to
animal keeping
Dictionary
[..]
Area. surface specialised for animal keeping.
Specifically, land parcels organised for animal
confinement. This area can consist of permanent or
semi-permanent structures such as buildings, shelters,
etc.. or it can be delimited with fences, walls or
boundary posts.
Information model – practical example
farm: an area organised by an operator
to perform activities related to
animal keeping
Dictionary
[..]
Area. surface specialised for animal keeping.
Specifically, land parcels organised for animal
confinement. This area can consist of permanent or
semi-permanent structures such as buildings, shelters,
etc.. or it can be delimited with fences, walls or
boundary posts.
Information model – practical example
Step 2: Spatial Characteristic
[..] all areas dedicated to animal
containment that are characterised by the
presence of physical delimitation [..]
physical delimitation can be composed of man-made
constructions such buildings, shelters, fences, walls,
electric fences and natural barriers that functionally
are used to contain the animals
Information model – practical example
Step 3: Primitive and attributes
Trade off:
Information model – practical example
Step 3: Primitive and attributes
Method:
Primitive:
Direct vs Indirect
Polygon vs Point
Information model – practical example
Step 3: Primitive and attributes
Data independence principle
• to assign a code to the farm (join function)
• to know when the spatial data was captured
• to know which capture method was used
• to know who captured the spatial data
• other geographical ancillary information (e.g.: address)
Information model – practical example
Step 4: evaluate the data quality
• For a sample of not less than 10% of captured farm
evaluate the spatial accuracy by means of a
“different data capturing method”
• Calculate the error as the distance between the
locations obtained by the two different methods for
the same object. The mean, the minimum and the
maximum distances of the sampled farms provide
us a sort of quality value for the collected data
Information model – practical example
Questions?
How best georeference a farm?
1) Geocoding
2) Direct
3) Indirect
How best georeference a farm? - Geocoding
How best georeference a farm? - Geocoding
You need:
• Address locator software
• Background-address map.
OpenStreetMap is a collaborative project to create a
free editable map of the world (Open Data Commons
Open Database License).
Google maps must be used according to the Google
terms of service
How best georeference a farm? - Geocoding
How best georeference a farm? - Geocoding
How best georeference a farm? - Direct
How best georeference a farm? - Direct
How best georeference a farm? - Direct
How best georeference a farm? - Indirect
How best georeference a farm? - Indirect
How best georeference a farm? - Indirect
How best georeference a farm?
Questions?