GIS data models: how to georeference a farm? Nicola Ferrè

Transcription

1 GIS data models: how to georeference a farm? Nicola Ferrè

2 The spatial characteristics of an object..there are many ways to spatially describe a farm.. definition Observer 1 Observer 2 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 scalable same shape for whole scales multi-scale spatial represetnation

3 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.

4 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.

5 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

6 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

7 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

8 Information model Spatial characteristic: to consider only the essential spatial elements that characterize the object o 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"

9 Information model

10 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

11 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)

12 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

13 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 realworld object

14 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).

15 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

16 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:

17 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..

18 Information model Questions?

19 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

20 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

21 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.

22 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.

23 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

24 Information model practical example Step 3: Primitive and attributes Trade off:

25 Information model practical example Step 3: Primitive and attributes Method: Direct vs Indirect Primitive: Polygon vs Point

26 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)

27 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

28 Information model practical example Questions?

29 How best georeference a farm? 1) Geocoding 2) Direct 3) Indirect

30 How best georeference a farm? - Geocoding

31 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

32 How best georeference a farm? - Geocoding

33 How best georeference a farm? - Geocoding

34 How best georeference a farm? - Direct

35 How best georeference a farm? - Direct

36 How best georeference a farm? - Direct

37 How best georeference a farm? - Indirect

38 How best georeference a farm? - Indirect

39 How best georeference a farm? - Indirect

40 How best georeference a farm? Questions?