You will continue your trip in this blog and discover the capabilities of GIS that enable it to be used as a spatial decision-making tool. “Spatial queries” are one of the crucial steps in the process. The various facets of spatial queries are covered in this lecture. In order to locate spatial objects, the goal of spatial inquiries and their analysis is to identify spatial links between elements of one or more topics. Such analysis’s findings can be applied to decision-making. A GIS’s database structure makes it possible to store and handle data in a logical, consistent, and organized manner.
Tables are used for storing both geometric and thematic data. The phrase “data analysis” refers to all of the research, questions, assessments, and other activities that are done on organized and stored spatial data in the field of geoinformation. The fundamental components of this structure—tables, fields, data sets, values, and connections—are used to access the data when a query is run to retrieve and respond to a spatial query. Dolci (2016). Many times, the software capabilities that are available also dictate how simple or sophisticated the query is.
The users’ needs and comprehension of the Geographic Information System’s capabilities come first. The types of queries that GIS can and/or does handle are covered in the section that follows.
Query a Step towards Information System
One of the primary functions of a geoinformation system is to infer new information from preexisting geographical data. Every spatial analysis entails the expert interpretation of the findings. Spatial analysis is the process of analyzing and synthesizing spatial data into a cohesive whole. (Bill 1999) “. Multiple queries that center on a distinct system, where the question and response system is designed in a system that is a repository of a data set, are what you need to build using GIS. As we already know, the geographic information system uses many queries to interact with tools, algorithms, and technologies in a computerized environment.
This makes it possible to handle big data sets and turn unprocessed data into information that can be used. “If the data are geographically referenced, the system is called a geographic information system (GIS).” “GIS is made up of a number of separate parts. While some of these features are fundamental, others are more intricate or necessary for certain uses. Important roles are played by the data management system, query functions, and user interface. The user can interact with the system through the user interface. Users can initiate procedures, query data, and more with its help. Analysis functions can be carried out by obtaining the data through the user interface. The database management system controls both data access and data management in general (Carosio 2000).
Spatial and aspatial data are the two categories of data that are utilized in GIS. This serves as the foundation for any query construction layer.
The association of spatially directed geometric information and theme-driven thematic data makes up the data structure. Without a doubt, the frame of reference that has spatial connotations is where geometry is conveyed. It is crucial to realize that, depending on the goal, any object, region, or phenomenon that one wants to map and investigate has a spatial reference. Depending on the goal of the spatial investigation, the extent may be smaller or larger. Geo reference, which indicates the precise locational scope of geographical information, is another name for spatial reference.
Classification of Queries
A. Using spatial and a spatial references
It is crucial that we comprehend that the following factors form the basis of each query:
Location-specific attributes
Topological qualities and metric properties (geometry).
Thematic characteristics
Information concerning, for example, neighborhood relations (what item is neighboring?), containedness (does an object contain other objects?), overlap (is an object overlapped by other objects?), etc., are examples of topological features. Each item is given thematic qualities in addition to geometric and topological ones. Tables are used to store them. Thematic and geometric data are interdependent. These alleged items are the topic.
According on the aforementioned characteristics, there are three possible methods for executing a query. A thematic inquiry, which is centered on a single or specific theme, can be one of them. A query can say, for instance, “Select all rhododendrons” from the provided image or “select all springs” that are situated within the specified spatial unit or image. A Geometric Query might be the second option, in which the selection process is based on a specific query pertaining to a geometric parameter. For instance, “select all the industries that are located less than 100m away from the river Ganges” or “select tobacco shops located within 100m near schools” are similar examples. The “condition criteria” pertaining to the surrounding spatial attributes and spatial interactions are taken into consideration in the third, which can be a topological query.
B. Queries based on the coverage of Data Sets
Sometimes data sets are so big that it is not possible to run a query on them all, and other times it is not necessary to cover the entire set. As a result, queries based on the datasets’ coverage could be run on all of the data with complete coverage or on a subset of the data, which is a specific section of the data. These are created using full queries and are referred to as subqueries. A “Select Statement” made up of three sections is called a subquery.
C. Query based on Access and Result
Direct Query
Manipulation
a straightforward question, The user or an application program can interact with the data. Consequently, it is possible to extract a subset while keeping the original data unaltered. You can input the selection commands in:
inquiry masks or command lines.
command line combinations (batch, macro).
formal language for queries. Structured Query Language (SQL 2)
On the other hand, “new geographic information elements can be created through manipulation.” In subsequent steps, these new elements can be employed for analysis. Generally speaking, the new objects must first be conceptually modeled, then the GIS must implement their data structure. A minimum data structure (without thematic features) can be automatically generated by some GIS. Combining various items can produce new information. They can be applied to more research (Claudia, 2016).
D. Different Queries
Spatial and attribute data are kept in two different files in a GIS. An identification number connects corresponding entries in the two files (for instance, a map of property parcel borders and the associated data, such as the owner’s name, the structure, and the structure’s value). This enables attribute data to be searched and displayed by a GIS according to spatial criteria, and vice versa. For instance, a GIS user can request that the GIS locate the relevant property parcel on the map by providing a record in the attribute database, or they can point to a specific property and ask the GIS to retrieve and show the attribute data of that parcel (Sidiqui, 2016).
Additionally, GIS can handle even more complicated queries. Relational operators are utilized for text attributes, all-numeric attributes, and other data types since they are so crucial to GIS. Table 2 contains a collection of relationship qualities. By creating a “query statement,” users can provide search parameters that include arithmetic and logical expressions. The value to be found is specified using operators like +, -, =, not =, <, <=, >, >=, between, and others. A single query can be executed by combining many query statements.
For instance, “How many structures are for sale in a specific location at a price of RS 12,00,000 or less?” A query statement would be created by the GIS and sent to the DBMS, which would then look through the attribute database to find the parcels that fit the requirements. The parcel numbers would then be sent back to the GIS by the DBMS. “After locating these parcels and their coordinates through a search of its spatial data file, the GIS would highlight those parcels on the property parcel map display.” However, GIS users can also request that the GIS retrieve the attribute data of every parcel located within a designated area by describing that area on the parcel map.
This space could take on any form. To focus the search or even to indicate which properties to get, logical operators could be used.
Features of a spatial item in geographic space are related to spatial queries in GIS. It might be a polygon, line, or point. Making a query set based on the spatial relationship of map features is how spatial queries are carried out. The spatial relationships between map features are defined by the spatial operators in the queries. Complex spatial inquiries can be solved by combining the majority of spatial operators, including overlaps, entirely contains, entirely contained by, contains, contained by, terminates in, terminus of, passes through, passed through by, on boundary of, has on boundary, touches, meets, and spatially equal.
According to Korte (1997), proximity operators that cannot be mixed are between, within, beyond, fully between, entirely inside, and entirely beyond. A disaster management agency in a region, for instance, might compile a database of all location addresses and use a spatial query to divide them into seismic zone 3 and 4 and non-seismic zone areas. Another example is shown in table 4, where a graphical input image with unique IDs generates a graphical output image based on a set of associations and a spatial query.
