gis data models: how to georeference a farm?

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?