Want to become GIS expert: Master these 20 Essential GIS Skills.


This article is inspired by a book by Gina Clemmer, “The GIS 20 Essential Skills” published by ESRI in 2017. This book offers an activation code for free GIS trail for 180-days, so it’s worth buying this book.

First thing first, you need to have basic knowledge on GIS in order to learn these skills. If you are new to GIS, and/or want to learn more about GIS, then check my blog, “Top 29 GIS Interview Questions that can help you land your dream job!!!” to learn most frequently asked GIS questions.

So, what are the 20 Essential GIS skills? Let’s talk about them:

1. Downloading Shapefiles6. Creating thematic maps11. Editing16. Joining boundaries
2. Creating basic maps and layout.7. Working with data tables12. Creating attribute queries17. Working with aerial photography
3. Projecting shapefiles8. Address mapping13. Creating location queries18. Creating reports
4. Preparing data for ArcMap9. Creating a categorical map14. Using geoprocessing tools19. Sharing works
5. Joining data to maps10. GPS point mapping15. Creating geodatabases20. Publishing maps
20 Essential GIS skills

1. Downloading Shapefiles and using essential ArcMap tools

1.1 What are Shapefiles?

Shapefiles are spaghetti data models containing a features class composed of points, lines, or polygons, but never a mixture. The attributes are stored in dBase file. Shapefiles can store multipart features, in which a single feature includes multiple objects. Check “What are Shapefiles?” to learn more about shapefiles, shapefile components and limitations of shapefiles.

1.2 How to download shapefiles?

There are so many websites that offer wide range of Free GIS datasets. You just need to find which one offers the datasets that you are looking for.

If you are in the USA, check “Important Sites to Download Freely Available GIS Datasets – In the USA” to find all different kinds of datasets. This blog has listed more than 100 web links where you can find free GIS datasets. For your ease, these links are categorized into different groups such as General, Boundaries and Shorelines, Landcover, Geology, Hydrology, Census, Elevation, Weather and Climate, Ecology, History, Crime and Justice, Power and Energy, Transportation, State-specific, and City of Region Specific.

If you are outside of the USA (or have different study area than USA), then check, “Important Sites to Download Freely Available GIS Data-sets Across the World!” where you will find a list more than 300 web links to download GIS datasets for almost all countries.

If you have a global study area, then check, Important GIS Data Download Sites where you will find a list of more than 100 web links to download GIS datasets for free. For your ease, these links are categorized into “Physical and Human Geography”.

1.3 What are different data formats?

It is always good to learn and know about the different data formats because 1. it saves your time while downloading and preparing your datasets, and 2. it helps you determine what tools and techniques you will be using. There are two data formats that GIS is handy with: Vector and Raster data formats. Both data systems store spatial and attribute data, but in different ways. Both are georeferenced, meaning that the information is tied to a specific location on the earth’s surface using x-y coordinates defined in a standard way: a coordinate system. Check, “What are different Data Formats in GIS?“ to learn more about these data formats.

1.4 Others

There are some other things that you need to know/learn including adding files to ArcMap, exploring the ArcMap interface, essential tools, table of contents, viewing and customizing data, creating geo-databases, and saving your project. Make sure to check “The GIS 20 Essential Skills” book and master these skills.

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2. Creating basic maps and layout.

The other big thing in GIS is to be able to create basic maps and designing the layouts. The skills include changing the layer colors; adding layers and labels; creating a layout; inserting title, legends, scale bar, north arrow, and source using text.

The more you paly with ArcMap, the more you will learn about these techniques.

3. Projecting shapefiles

One of the most important and most confusing (to most people) things is projecting the datasets in correct projection. Often people confuse with Geographic and Projected Coordinate systems and end up messing up with their projects. When I was a beginner, I chose to start over than to project the layers into the right projection. Once you learn it, your life become much easier.

3.1 What is projection? What are the projecting tools in ArcMap?

Projections is the method to give shapefiles the correct shape, size, direction, and distance. Defining projection ensures that the geography is reflected properly, the distance is recorded correctly, and all the layers are visible. It is also important that you know what tools to choose while projecting the shapefiles. ArcMap offers various tools like Project Tools and Define Projection, is will be wise to know which one to use when. Check, “What are the differences between Project Tool and Define Projection?” to learn when to use what tools.

3.2 What are the different projection systems in GIS?

Depending upon the representation of the surface, one should be able to choose either of these two coordinate systems: the geographic and projected coordinate system. If you consider the earth as a 3-Dimensional plane, then geographic coordinate system comes into the play whereas if you consider the earth as 2-Dimensional surface, then projected coordinate system comes into play. Check, What are the differences between Geographic and Projected Coordinate Systems?to learn about coordinate systems, the differences between Geographic and Projected coordinate systems, and when to use which coordinate system.

ArcMap offers other varieties of projection systems. Make sure to learn all these.

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4. Preparing data for ArcMap

Map making is all about data manipulation and visualization. The more you practice, the better you become. Whether the data be in vector or raster format, or even .csv, excel your skills to manipulate them. Not all the time you get ready-to-go data. You need to master the techniques to convert one data format to another, eg. Raster to vector or vice-versa; incorporate one data file with another, eg. Merging excel dataset into shapefiles; data cleaning and more.

The big questions it where do we get these data from?
Check these blogs to learn where to find what data: Important Sites to Download Freely Available GIS Datasets – In the USA, Important Sites to Download Freely Available GIS Data-sets Across the World!, and Important GIS Data Download Sites where you will find a list of more than 500 web links to download GIS datasets for free.

5. Joining data to maps

This is one of the most frequently used techniques in GIS. Joining could be either joining excel spreadsheet to a shapefile, or a shapefile to shapefile, an attribute table to another—what-so-over the beauty of joining the datasets is it gives better visualization of the distribution of data.

5.1 Joining tools in ArcMap

Typically, you can perform a join with either the Join Data dialog box, accessed by right-clicking a layer in ArcMap, or the Add Join tool. While joining, you’ll join a table of data to a layer based on the value of a field that can be found in both tables. The name of the field does not have to be the same, but the data type has to be the same; you join numbers to numbers, strings to strings, and so on.

5.2 Basic considerations while joining data to maps

Things to consider while performing the joins.

  • Field properties, such as aliases, visibility, and number formatting, are maintained when a join is added or removed.
  • Field names should to start with a letter.
  • Field names should only include alphanumeric characters or underscores.
  • None of these: `~@#$%^&*()-+=|\, <>? /{}.!'[]:;
  • No spaces (That includes before the field name, in the middle, or after it.
  • Field names will be cut off after 64 characters
  • Reserved words should be avoided.

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6. Creating thematic maps

A map that focuses on a specific theme or subject area is a thematic map. Thematic maps are made for specific task and may include a variety of different map types including choropleth maps, dot maps, heat maps, isorhythmic maps, animated time-series maps, and proportional symbol maps.

“Thematic maps pull in attributes or statistics about a location and represent that data in a way that enables a greater understanding of the relationships between locations and the discovery of spatial patterns in the data that we are exploring.”


There are few techniques that you need to master to create a great thematic map. These skills include, but not limited to: mastering the color ramps; fixing the percentages; changing the legend breaks, labeling the features, fixing the legends, and more.

7. Working with data tables

Learning how to manipulate the attribute tables by adding or deleting columns, editing values, and performing calculations are equally fun as much as it is important. There are different techniques to edit raster and vector datasets. Some of the most general techniques of editing vector datasets include adding and deleting columns and rows, joining attribute tables, changing legend breaks, clipping, buffering, and so on; whereas some general techniques of editing raster files include: reclassification, mosaicking, extracting by mask, and so on.

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8. Address mapping

Often referred to as Geocoding, it is the process of associating an address or a place name with coordinates on the map. In a spatial database this is done as a point layer with name of the place as an attribute to the point location. This is one way of geocoding. For addresses, the associated coordinates are not saved in a database directly but computed using a method called linear referencing. (Thus, the confusion between the terms geo-referencing and linear-referencing). The start and end addresses along a line segment are saved and intermediate addresses are interpolated and the coordinates are calculated.

Most people confuse Geocoding with Georeferencing. Georeferencing is the process of taking a raster image or vector coverage, assigning it a coordinate system and coordinates, and translating, transforming, and warping/rubber sheeting it into position relative to some other spatial data, such as survey locations, street intersections, etc. If you are confused too, please check, What are the differences between Geocoding and Geo-referencing? that explains the differences between geocoding and georeferencing.

To be able to geocode in ArcMap using ESRI’s address locator, you need to have ESRI credits—which you can either buy from ESRI or obtain from your organization. Or you want to geocode by creating your own address locator, then yes, there are ways—you just need to find the techniques and be prepared to spend a lot of time.

9. Creating a categorical map

Categorical mapping similar to thematic mapping—only the difference is: thematic mapping uses color shading to indicate values whereas in categorical mapping values represent categories instead of numbers. Categorical mapping works with point, line, and polygon data types; points—to map crimes (burglaries and assaults); lines—to map different streets or rivers; and polygon—to map land-use zoning categories (residential, commercial, and industrial).

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10. GPS point mapping

In addition to geocoding—which is associating an address or place name with coordinates on map, you can also map the longitude and latitudes (x,y) coordinates of the data collected from the ground using Global Positioning System (GPS). The GPS, originally NAVSTAR GPS, is a satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of the global navigation satellite systems (GNSS) that provides geolocation and time information to a GPS receiver anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. Obstacles such as mountains and buildings block the relatively weak GPS signals. The GPS does not require the user to transmit any data, and it operates independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the GPS positioning information. The GPS provides critical positioning capabilities to military, civil, and commercial users around the world. The United States government created the system, maintains it, and makes it freely accessible to anyone with a GPS receiver.

GPS point mapping is often used in environmental research to map point data such as water samples, animal tagging, invasive plant species, and others.

11. Editing

Editing maps includes, but not limited to, changing boundary lines, merging polygons, creating shapefiles, clipping, buffering, appending shapefiles to each other, and many more. The editing is done as per the requirements of the project or task.
Some of the most common editing tasks are:

  • Creating new feature classes
  • Creating new shapefiles [Confused about feature class and shapefiles? Check, What are the similarities and differences between Shapefile and Feature Class?]
  • Editing existing shapefiles—creating new shapefiles from existing ones
    o Creating new features on an existing shapefile
    o Adding or removing columns (fields) and rows
  • Editing the boundary lines
  • Moving polygons
  • Merging polygons
  • Converting polygons to points

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12. Creating attribute queries

Somewhat related to editing shapefiles, the skills of creating attribute tables are one of the most important skills in GIS. An attribute query is the process of searching and retrieving desired records of features from the database. There are several tools in ArcMap that facilitates the attribute queries—one of the most popular is, Select by Attributes. Select by Attributes allows you to provide a SQL query expression that is used to select features that match the selection criteria. Other querying tools are Select by Location (discussed in chapter 13), Select by Graphics, etc.

The task of queries includes, but not limited to, searching strings, searching and eliminating null values, querying numbers—sorting ascending and descending order, doing mathematical calculations, querying dates, creating subsets of feature classes, and more.

13. Creating location queries

Similar to creating attribute queries—but the difference is that location query does not involve selecting data. A location query involves selecting geographies with other geographies. This type of query is usually used to query geography and works equally well with point, line, and polygon data to find locations.

We use Select by Location for this kind of query. The Select by Location tool lets you select features based on their location relative to features in another layer. For instance, if you want to know how many homes were affected by a recent flood, you could select all the homes that fall within the flood boundary. Some of the queries this tool does are: intersect, are within the distance of, are within, are completely within, contain, completely contain, have their centroid in, share a line segment with, touch the boundary with, are identical to, are crossed by the outline of, and more.

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14. Using geoprocessing tools

14.1 What is geoprocessing?

Geoprocessing is a framework and set of tools for processing geographic and related data. The comprehensive suite of geoprocessing tools can be used to perform spatial analysis or manage GIS data in an automated way. Geoprocessing is for everyone that uses ArcGIS Pro. Whether you are a new or advanced user, geoprocessing will likely be an essential part of your day-to-day work.

A typical geoprocessing tool performs an operation on a dataset such as a feature class, raster, or table, and creates a resulting output dataset. For example, the Buffer tool takes features as input, creates buffer areas around the features to a specified distance, and writes those buffer areas to a new output dataset.
In addition to the suite of tools, geoprocessing is also a powerful framework that supports control of the processing environment and allows you to build custom tools that can further automate your work. You can use the geoprocessing tools included in ArcGIS Pro as building blocks to create an infinite number of custom tools that automate repetitive tasks or solve complex problems.

14.2 What are the geoprocessing tools?

There are literally hundreds of geoprocessing tools available. Some of the most common and most important geoprocessing tools are:

  • Buffering–uniform distance around a feature (point, line, or polygon)
  • Merging–combining two files
  • Unioning–the union tool differs from the merge tool in that each record in the attribute table is maintained for each merged item; however, the visible boundary between the polygons disappears.
  • Appending–combines multiple shapefiles into one shapefile.
  • Clipping–clip one boundary by using the outline of another boundary
  • Dissolving–creates larger regions out of similar regions
  • Overlay and proximity– What’s on top of what? and What’s near what?
  • Surfaces Analysis—deals with continuous data
  • Spatial and nonspatial statistics– such as minimum, maximum, sum, frequency, mean, and standard deviation
  • Table management– such as adding or deleting fields, creating relationships between tables, or creating features from columns containing coordinates
  • Selection and extraction– to reduce or extract data from larger, more complex datasets.

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15. Creating geodatabases

15.1 What is a file geodatabase?

geodatabase is a database designed to store, query, and manipulate geographic information and spatial data. It is like a container in which you can store all files related to your GIS project. You can store multiple shapefiles, aerial photographs, spreadsheets, and many other types of files. It helps manage your files together and makes it easier to share your files to others.

You may want to or may not want to create geodatabase based on the size of your project—if your project is small and has fewer files, then it’s not so important to create geodatabase; but as your project grow bigger it is important to create geodatabase.

15.2 Why is geodatabase useful?

Here are top 9 nine reasons to use file geodatabase:

  1. Improved versatility and usability
  2. Optimized performance
  3. Few size limitations
  4. Easy data migration
  5. Improved editing model
  6. Storing rasters in geodatabase
  7. Customizable storage configuration
  8. Allows updates to spatial index settings
  9. Allow the use of data compression

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16. Joining boundaries

A spatial join involves matching rows from the join layer to the target layer based on a spatial relationship and writing to an output feature class. When a match is found during processing, a row is added to the output feature class containing the shape and attributes from the target layer and the matching attributes from the join layer. The spatial relationship is determined by the geometry types of the input layers as well as the chosen match option. The table below describes the spatial relationships.

From ArcGIS Desktop documentation:

  • A spatial join involves matching rows from the Join Features to the Target Features based on their relative spatial locations.
  • By default, all attributes of the join features are appended to attributes of the target features and copied over to the output feature class. You can define which of the attributes will be written to the output by manipulating them in the Field Map of Join Features parameter.
  • Two new fields, Join_Count and TARGET_FID, are always added to the output feature class. Join_Count indicates how many join features match each target feature (TARGET_FID).Another new field, JOIN_FID, is added to the output when JOIN_ONE_TO_MANY is specified in the Join Operation parameter.
  • When the Join Operation parameter is JOIN_ONE_TO_MANY, there can be more than one row in the output feature class for each target feature. The JOIN_FID field makes it easier to determine which feature is joined to which target feature (TARGET_FID). A value of -1 for JOIN_FID field means no feature meets the specified spatial relationship with the target feature.
  • All input target features are written to the output feature class only if:
    • The Join Operation is set to JOIN_ONE_TO_ONE, and
    • Keep All Target Features is checked (join_type = “KEEP_ALL” in Python).
  • Merge rules specified in the Field Map of Join Features parameter only apply to attributes from the join features and when more than one feature is matched to a target feature (when Join_Count > 1). For example, if three features with DEPTH attribute values of 15.5, 2.5, and 3.3 are joined, and a merge rule of Mean is applied, the output field will have a value of 6.1. Null values in join fields are ignored for statistic calculation. For example, 15.5, <null>, and 2.5 will result in 9.0 for Mean and 2 for Count.
  • When the Match Option is set to CLOSEST or CLOSEST_GEODESIC, it is possible that two or more join features are at the same distance from the target feature. When this situation occurs, one of the join features is randomly selected as the matching feature (the join feature’s FID does not influence this random selection). If you want to find the 2nd, 3rd, or Nth closest feature, use the Generate Near Table tool.Learn more about how proximity is calculated
  • If a join feature has a spatial relationship with multiple target features, then it is counted as many times as it is matched against the target feature. For example, if a point is within three polygons, then the point is counted three times, once for each polygon.
  • For more information about using the three-dimensional spatial relationships INTERSECT_3D and WITHIN_A_DISTANCE_3D see Select by Location 3D relationships.

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17. Working with aerial photography

Aerial photography (or airborne imagery) is the taking of photographs from an aircraft or other flying object. 

“For the mapping of terrestrial features, aerial photographs usually are taken in overlapping series from an aircraft following a systematic flight pattern at a fixed altitude. Each photograph depicts an area that includes several control points, the locations of which are determined by ground-surveying techniques. A technique known as photogrammetry (q.v.), which involves the simultaneous projection of the overlapping views, makes possible the preparation of contour maps or three-dimensional models of the terrestrial surface that has been photographed. Valuable data on topography, geology, hydrology, soil and vegetation, meteorology, ocean currents, and fish resources have become accessible with the use of satellite technology and expert interpretation. Views of cloud patterns obtained from orbiting satellites are valuable in weather forecasting. Aerial photography also has vital military reconnaissance and intelligence-gathering applications.”


Also check, What is the importance of GIS (Geographic Information Science) in Remote Sensing? to learn about the relationship between GIS and Remote Sensing.

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18. Creating reports

Creating reports is as important as doing all the technical stuffs in ArcGIS. Reports can give your readers a lot of information and provide credibility for map’s data.

19. Sharing works

Sharing works could be sharing the final maps, or sharing layers, or tools, or even geodatabase. The habit of creating geodatabase comes in really handy here–if you are working in a group and are sharing your work a lot.

20. Publishing maps

Publishing maps is another way of sharing the maps. ArcGIS online provides a space for users to upload and download maps, data, packages, and all sorts of other useful stuff. Another way of publishing maps could be geoenabled PDFs since it allows you to package the underlying data along with the maps, which in turn allows the users to click the map and access attribute data.

Other options to share your maps can be sharing using social media, sharing using web, etc.

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20 thoughts on “Want to become GIS expert: Master these 20 Essential GIS Skills.”

  1. Thanks a lot for this article. Sorry if I missed it the text but programming is also a key skill for GIS Expert nowadays (whether in Python or R or now Arcade). Also, as we are moving towards a more connected world, web development skills also matters (HTML, Javascript…). With that being said
    I really appreciated your 20 skills.

    1. You are right! The use of coding has made mapping more easier and efficient. And we can see the world moving towards web mapping and stuffs and really cool things in real time which otherwise was nearly impossible for desktop version. It is important to master these 20 skills and try and implement the coding knowledge to compete with the changing world! Good luck!

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