A GIS or Geographical Information System is a framework for the collection, management, analysis, and presentation of geographical details. GIS data results from this system. GIS data is essential for effective decision-making in such areas as petroleum, urban planning, mining, environmental science, and so many other areas.
There are three main types of vector data in GIS:
Polygon data uses polygons to represent areas like the boundaries of a city, forest, or lake on a larger-scale map. These features are two-dimensional and can, therefore, be used to determine the area of the geographical feature they are representing. Polygon features are distinguished using colors, patterns, numeric or color gradation, or any other scheme.
Line, also known as arc data, is used to represent features that have a more linear characteristic, such as rivers, streets, and roads. Since they have one dimension, a user can determine the length using the scale provided on the map. Line features usually have a start and end point. The kinds of symbology used to distinguish among line data include line types (dotted, straight, dashed, etc.), colors, and line thickness. For instance, any hydrological features like streams and rivers are represented with thin blue lines while roads are represented with a solid black line.
Point data is used on GIS data to represent discrete detailed points or nonadjacent features. Since these points have no dimensions, you may not use them to determine the area of the represented feature. Features represented by these points include schools, hospitals, water treatment plants, and culverts locations. Point and line data include features that can be represented using polygons at a much smaller scale to reduce clutter on the map. The user may zoom in to get more details on the feature represented by a point, such as buildings and footpaths in a school. If the user requires a higher degree of spatial resolution, a street curb width file can be obtained, which will show details like the width of a road or pathway and rights of way.
Raster data is also called grid and is used in GIS data to represent the fourth kind of feature that maps have: surfaces. Raster data is cell-based and is also used to show satellite and aerial imagery. There are two main types: discrete and continuous. Continuous data examples would be temperature and elevation, while discrete data would be the population density.
Unlike vector, raster data is created by each cell, receiving the value of the feature that dominates the cell. As the user moves through the map, the value of one cell will transit into another as they move through different cells.
For instance, dark green cells may represent dense vegetation, and as you move from a densely forested area into an urban setting, the cells change the color gradually from the dark green to a lighter green, then light pink to represent developed land.
Shapefile, abbreviated as SHP, is a file format for vector data in any GIS system used to store the location, shape, and attributes of geographical features. This format is built and modulated by Esri as an open specification for data interoperability among itself and other GIS firms. Shapefile is usually stored in a collection of related files and has one feature class. Shapefile is the most common geospatial file type you will encounter and is the industry standard. To make a shapefile, you will require a set of mandatory files in the .shp format, which are Esri files that have their specific geometries. Every Shapefile has its own .shp file that represents its own spatial vector data, say points, lines, or polygons.
.dbf is a standard database file used to object IDs and store attribute data. For shapefiles (.shp), .dbf files are mandatory. Users can readily open a .dbf file using Ms. Excel or Access.
.shx are mandatory Esri and AutoCAD shape index position files. With this file, a user can search forward and backward.
Unlike the file formats listed above, .prj files are optional, and are used to store the metadata associated with shapefiles’ coordinate and projection system. Without this file, you will encounter the error ‘unknown coordinate system.’ To fix this error, you have to use the ‘define projection’ tool to help you generate the .prj files.
.xml file types are optional and also contain essential metadata associated with the shapefile. If you accidentally deleted this file, you will delete the file’s metadata. You can open this kind of file using any text editor.
.sbx file formats are optional spatial index files that optimize spatial queries. This file type is saved together with a .sbx file, and both make up and shape index file that will speed up spatial queries in a GIS system. Where both .sbx and .sbn files exist, loading times are up to six seconds faster.
.cpg are optional plain text files that describe how your shapefile is encoded. Without the .cpg file, your shapefile gets the system’s default encoding.
The GeoTIFF is an industry image standard file for satellite remote sensing and GIS technology. GeoTIFFs are often accompanied by other files, including:
Geometry is a branch of mathematics that deals with spatial relationships, measures, the properties of surfaces, lines, and points. In a GIS system, vector geometry is used to represent the spatial aspect of geographical features with discrete boundaries like states, rivers, lakes, parcels. Examples of such geometry include:
A point has x and y fields along a spartial Reference field. The x shows the location of a point along the x-axis and y the point's location on the y-axis. The spatial Reference defines the system used to locate the model of the Earth. A point may also have m and z fields, where the m shows a random linear measurement independent of the point’s location, and z shows elevation.
Polylines are showing lines between two and above points, where the line can represent walls, barriers, roads, and routes between two places. These have two major characteristics:
Paths: a collection of paths, where every path is a list of coordinates in [x, y] format, and spartialReference that describes the measurement system used to identify the polygon on a model of the Earth.
Polygons are used to stand for enclosed shapes like states or cities that are closed because they have boundaries. Polygons have a couple of main properties: Rings, where both clockwise and anticlockwise rings are regarded as holes. Each ring is an array of [x, y] coordinate pairs, and the spartialReference that plays the same role in Polylines and points.
Extents show rectangular shapes used to ground a map on a particular region. Extents also called envelops, have five main characteristics:
Here are a few places where you can get the best free GIS data:
The Esri Open Data Hub is a goldmine of free data. As of 2020, this GIS website provides its users with over 250,000 datasets from over 5000 organizations. The Esri Open Data Hub is, therefore, the best source of reliable GIS data. You can also download the data in multiple formats.
Natural Earth Data, first, is in the public domain, which gives you the ability to use, modify, and share the data as you see the fit. You can also access all-important cultural and physical vector GIS datasheets without any hassle. If you are a cartographer, Natural Earth Data will be a goldmine for you.
USGS Earth Explorer is one of the best GIS websites for satellite and aerial imagery, and you can access it and download data from any location.
GIS technology makes it possible to analyze spatial locations and organize layers of information into 3D visualizations that are easier to interpret using maps and other resources. This kind of data can reveal patterns, relationships, crisis areas, situations, and opportunities that will help its users make better decisions.