GIS data management and storage

Author: Roman

Common file formats for GIS data

TIF

TIF files are raster image files. The suffix TIF or TIFF is a kind of OGC specification, full name GeoTiff. Tif raster image data’s coordinate system information is usually not viewable in the resource manager. GIS software is required to view the coordinate system information because it is written inside the data file.

Tif can have 8-bit depth, 24-bit depth, 24-bit for true color, and 8-bit for terrain data with only one height value. At present, a lot of satellite image data, terrain data storage is TIF.

SHP

Shapefile is a common format file of ESRI ArcGIS platform, and is an industry standard vector data file. Shapefile stores the non-topological geometric objects and attribute information in the spatial feature table in the data set. Geometric objects in the feature table are stored in the graph file represented by the coordinate point set –SHP file. Shapefile does not contain Topological data structure.

SHP features:

1. A Shape file consists of three files: main file (.shp), index file (.shx), dBASE table (.dbf)

2. An SHP file can only store one type of point, line or plane, and does not store in the mixed existence state

3. SHP can set many field properties

KML/KMZ

KML(Keyhole Markup Language) is an XML-based Markup Language originally developed and maintained by Keyhole, a company owned by Google. It uses XML syntax format to describe geospatial data (such as points, lines, faces, polygons and models). It is suitable for geographic information cooperation and sharing under network environment. In April 2008, the latest version 2.2 of KML was declared by OGC as an open geographic information coding standard and was maintained and developed by OGC.

A KMZ file is a compressed KML file. Because KMZ is a compressed package, it can contain not only KML text, but also other files associated with it such as images, models, and so on.

DWG/DXF

DWG file: is Autodesk AutoCAD platform graphics file format, is two-dimensional or three-dimensional graphics files. DXF files can be converted to each other.

DXF file: an open vector data format for data exchange between AutoCAD and other software platforms

Since AutoCAD is the most popular CAD system, DXF is also widely used. Most CAD systems can read or output DXF files.

GeoJSON

GeoJSON is a format suitable for encoding various geographic data structures on the Web. It is a geospatial information data exchange format based on Javascript object representation. The difference from the normal JSON file format is that there are certain specifications for its attributes and composition.

GeoJSON divides all geographical elements into Point, MultiPoint. LineString, MultiLineString, Polygon, MultiPolygon, GeometryCollection First, these elements are encapsulated into a single geometry, and then put into a set of elements as Feature elements.

Data Organization Structure of GIS Software (SuperMap)

Take SuperMap as an example. Data organization structure mainly includes workspace, data source, data set, map, scene, layout, etc.

• Data source collections: Organizes and manages all data sources in a workspace. Data sources are collections of data sets composed of various types of data such as point, line, plane, raster/image data. A data source may contain one or more sets of different types of data; It is also possible to store both vector and raster datasets.

• Map collection: Used to manage the map data stored in the workspace. The maps displayed and made by the user in the workspace can be saved in the workspace for easy browsing the map the next time they open the workspace.

• Layout collection: Used to manage the layout data of the workspace. Layout is mainly used for typesetting and printing maps.

• Scene collection: Used to manage the scene data stored in the workspace, where the scenes displayed and created by the user can be saved.

• Resource collection: symbol library collection, used to manage symbol library resources used in maps and scenes in the workspace, including point symbol library, line symbol library, and fill symbol library.

The workspace

That is, the user’s working environment. When performing data operations, users need to create a workspace before they can further operate GIS data. The workspace will save the user’s operation results in the working environment, including the data source opened by the user in the workspace, the saved map, layout and 3D scene, etc. When the user opens the workspace, he can continue to work on the previous work results.

The map, layout, 3D scene and resources in the workspace are all attached to the workspace, that is, these contents are saved in the workspace. When the workspace is deleted, the map, layout, 3D scene and symbol library resources in the workspace are also deleted accordingly. The data source is stored independently and is only associated with the workspace, but not stored in the workspace. When deleting a workspace, the association between the workspace and the data source is deleted, but the data source cannot be deleted.

Data source collection

The data source collection in the workspace mainly manages all the data sources opened in the workspace. Through the data source collection in the workspace, the operation functions such as creating, opening and closing data sources can be realized.

The data source

Data sources are used to store spatial data, independent of the workspace, so all spatial data stored in the data source is also stored independent of the workspace.

Data sources can be divided into three categories:

• File data sources are UDB data sources and are stored in files with.udb/.udd extensions. When you create a UDB data source, two files are generated simultaneously. In addition to spatial geometry objects, GIS spatial data also contains attribute information of objects. In file data sources,.udb files mainly store spatial geometry information of spatial data, while.udd files store attribute information. A data source file corresponds to only one data source.

• Database-type data source is stored in the data source in the database, and the spatial geometry information and attribute information of its spatial data are stored in the database.

• A Web data source is stored on a server on the network. When using this type of data source, the corresponding data source is obtained through the URL address.

A workspace can contain multiple data sources of different types. Usually, one data source organizes spatial data for a specific purpose, so as to facilitate data classification and use.

The data set

Data source of spatial data is the abstraction of the real world, is in the real world geography abstract things for the computer can process all kinds of graphic objects in the world, in the real world dot things as abstract as point geometry object, linear things as abstract as the geometric objects, planar things as abstract as surface geometry object, in order to facilitate the unified management of data, The concept of data set is introduced, that is, similar things are stored in a kind of data set.

For example, a point data set can store only point geometry objects, a line data set can store only line geometry objects, and a plane data set can store only plane geometry objects. Thus, the spatial data in a data source is organized into data sets of various types, that is, the data source is actually a collection of data sets containing multiple data sets of various types.

The data set types of SuperMap GIS include: Point, Line, Region, Tabular, Network, CAD, Text, LineM, Image, raster number Data set (Grid), Model data set (Model).

Data set is one of the basic organization units of spatial data in SuperMap GIS and the smallest unit of data organization. Data set can be used as a layer to realize visual display in the map window, that is, geometric objects stored in data sets can be presented in the map window in the form of graphics. For raster and image data sets, According to its stored pixel value in the way of image display in the map window. And the visual editing of data sets is also realized through the map window, such as editing the spatial position and shape of geometric objects in data sets or obtaining new data sets through vectorization.

A data source can contain multiple data sets of various types. Data sources in a workspace can be used to manage data sets in a data source, including creating data sets or importing data from other sources as data sets, and other operations.

Map collections

The map collection is used to manage the map data stored in the workspace. The maps displayed and made by the user in the workspace can be saved in the workspace, so that the map can be easily viewed the next time the workspace is opened.

The application can open multiple map Windows at the same time, and each map window currently displays a map. The map in the workspace is included in the map collection. Because the map is saved in the workspace, the map can be saved only when the workspace is saved.

The map

Add the data set to the map window and assign display properties, such as display style, thematic map, etc., as layers. A map is created when one or more layers are stacked together in a certain order and displayed in a map window. In general, one layer corresponds to one data set; The same data set can be added multiple times to different map Windows and can be given different display styles. The style of the layer in the map window can be changed at any time according to the need, by changing the layer style or creating a thematic map two ways to achieve. In the map window, you can also edit the spatial geometry object in the layer visually, such as changing the position, size and shape of the object, etc. These operations will directly reflect the data set corresponding to the layer. In other words, the editing of the layer is essentially the editing of the data set associated with the layer.

Set the layout

A layout collection in a workspace manages all the layouts saved in a workspace, allowing you to create, save, export, print, and delete layouts.

layout

Layout is mainly used for typesetting and printing maps. It is a mixture of typesetting and layout of different elements such as maps, legends, map scales, Pointers and texts.

Scene collection

The collection of scenes in a workspace manages all the scenes saved in the workspace.

scenario

The scene is based on the abstract ball model to simulate the real earth, and the geographical things abstracted from the real world are displayed on the sphere, so as to reflect the actual spatial position and mutual relationship of the real geographical things more intuitively and vividly. Users can directly load 2d or 3D data onto the ball for browsing, making thematic maps, etc.

Resource collection

The resource collection in the workspace mainly manages the symbol library resources used by the maps in the workspace, including symbol library, linear library, and fill library.

The symbol library

Use the dot library to set the style of points on the layer, including symbol type, size, color, etc. Use the line symbol library to set the style of the line in the layer, including line type, line width, line color, etc. Using the Fill symbol library, set the fill style of the face object in the layer.

ArcGIS

The data organization structure of ArcGIS mainly includes GDB and MDB

Data formats supported by ArcGIS:

Map File (MXD)

That is, the user’s working environment. When performing data operations, users need to create a map file before further operating GIS data. The map file will save the user’s operation results, including the data source that the user is opening, symbolic scheme, etc. When the user opens the map file, he can continue his previous work.

Geodatabase A geographic database

Geodatabase is a new data model developed on the basis of new integrated data storage technology. Unified data management that all spatial data models (including Shape and Coverage) could not achieve before the implementation of the Geodatabase data model. That is, under a common model framework, GIS is generally processed and expressed in the geographic space features such as vector, grid, TIN, network and address unified description. At the same time, Geodatabase is an object-oriented geographic data model, and its expression of geographic spatial features is closer to our understanding and expression of real objects than previous models.

table

Tabular information is the basis of geographic elements and can be used to display, query and analyze data. In short, a table is made up of rows and columns, and all rows have the same column. In ArcGIS, rows and columns are called records and fields respectively. Each field can store a specific data type, such as a number, date, or text segment.

Factor data set

A factor dataset is a collection of related element classes that share a common coordinate system. Factor datasets are used to consolidate related factor classes by space or topic. Their main purpose is to organize related element classes into a common data set for constructing topological, network, topographic, or geometric networks.

Elements of class

Data source of spatial data is the abstraction of the real world, is in the real world geography abstract things for the computer can process all kinds of graphic objects in the world, in the real world dot things as abstract as point geometry object, linear things as abstract as the geometric objects, planar things as abstract as surface geometry object, in order to facilitate the unified management of data, Store similar things in a single element class. For example, the point element class can store only point geometry objects, the line element class can store only line geometry objects, and the plane element class can store only plane geometry objects.

Terrain Dataset is a multi-resolution tin-based surface data structure constructed from measurements stored as elements in a geographic database. Terrain datasets are typically constructed using lidar, sonar, and photogrammetric sources. Terrain is stored in the Terrain database’s elements dataset, which contains the elements used to build Terrain.

Network data set

Network data sets are ideal for building transportation networks. They are created from source elements that contain simple elements (lines and points) and turn elements, and store the connectivity of source elements. When the ArcGIS Network Analyst extension module is used to perform the analysis, the analysis always acts on the Network data set.

The topology

Topology relationships can enforce topology rules for a specified single or multiple element classes. For example, a block cannot overlap, a block cannot span two administrative divisions, and buildings must be within the block, etc., all of which are topology rules. These rules can be applied to these element classes after they are established. When data is edited for these element classes, ArcGIS will automatically conduct topology check.

Relationship between class

Is an association mechanism between one table (element class) and another table (element class). A relational class has a table (element class) pointing to another element class. When the data in the first element class changes, the data in the other element class changes. For example, we can associate the block with the building. When the block moves, the buildings in the block can move automatically with the block.

Grid directory

Raster data set

Raster data sets represent geographical elements by dividing the world into discrete square or rectangular pixels laid out on a grid. Each pixel has a value that represents some characteristic of the location, such as temperature, elevation, or spectral value.

A Mosaic dataset is a set of raster datasets (images) stored in catalog form and displayed or accessed as a single Mosaic image or a single image (raster). The total file size and number of data sets of these collections can be very large. Raster data sets in Mosaic data sets can be retained on disk in native format or exist in geographic databases. Metadata can be managed through raster records as well as properties in property sheets. By storing metadata as properties, it makes it easier to manage parameters such as sensor direction data, and it also speeds up queries on selected content.