Since all tracks are hosted on the web with HTTP/HTTPS links provided for submission as tracks, the webservers which are hosting the track files need Cross-Origin Resource Sharing (CORS) enabled.

Quoted from MDN:

Cross-Origin Resource Sharing (CORS) is a mechanism that uses additional
HTTP headers to tell a browser to let a web application running at
one origin (domain) have permission to access selected resources
from a server at a different origin. A web application makes a
cross-origin HTTP request when it requests a resource that has
a different origin (domain, protocol, and port) than its own origin.

Configure your webserver to enable CORS

Most likely the browser domain is different from the server the tracks are hosted on. The hosting server needs CORS enabled and for an Apache web server in Ubuntu this setup will work:

Header always set Access-Control-Allow-Origin "*"
Header always set Access-Control-Allow-Methods "POST, GET, OPTIONS, DELETE, PUT"
Header always set Access-Control-Max-Age "1000"
Header always set Access-Control-Allow-Headers "x-requested-with, Content-Type, origin, authorization, accept, client-security-token"

Prepare track files

The browser accesses track files from their URL. Only a portion of the data, that within the specific view region, are transferred to the browser for visualization. Thus, all the track files need be hosted in a web accssible location using HTTP or HTTPS. The following sections introduce the track types that the browser supports.

Binary track file formats like bigWig and HiC can be used directly with the browser.

bedGraph, methylC, categorical, longrange and bed track files need to be compressed by bgzip and indexed by tabix for use by the browser. The resulting index file with suffix .tbi needs to be located at the same URL with the .gz file.

Bed like format track files need be sorted before submission. For example, if we have a track file named track.bedgraph we can use the generic Linux sort command, the bedSort tool from UCSC, or the sort-bed command from BEDOPS. Here is an example command using each of the three methods:

# Using Linux sort
sort -k1,1 -k2,2n track.bedgraph > track.bedgraph.sorted
# Using bedSort
bedSort track.bedgraph track.bedgraph.sorted
# Using sort-bed
sort-bed track.bedgraph > track.bedgraph.sorted

Then the file must be compressed using bgzip and indexed using tabix:

bgzip track.bedgraph.sorted
tabix -p bed track.bedgraph.sorted.gz

Move files “track.bedgraph.sorted.gz” and “track.bedgraph.sorted.gz.tbi” to a web server. The two files must be in the same directory. Obtain the URL to “track.bedgraph.sorted.gz” for submission.

SAM files first need to be compressed to BAM files. BAM files need to be coordinate sorted and indexed for use by the browser. The resulting index file with suffix .bai needs be located at the same URL with the .bam file.

Here is an example command:

# Using samtools view to convert to bam
samtools view -Sb test.sam > test.bam
# Using samtools sort to coordinate sort the file
samtools sort test.bam > test.sorted.bam
# Using samtools index
samtools index test.sorted.bam

Annotation Tracks

Annotation tracks represent genomic features or intervals across the genome. Popular examples include SNP files, CpG Island files, and blacklisted regions.


bed format files can be used to annotate elements across the genome or to represent reads from a sequencing experiment. For more about the bed format please check the UCSC bed page.

Example lines are below:

chr9        3035610 3036180 Blacklist_155   .       +
chr9        3036200 3036480 Blacklist_156   .       +
chr9        3036420 3036660 Blacklist_157   .       +

Every line must consist of at least 3 fields separated by the Tab delimiter. The required fields from left to right are chromosome, start position (0-based), and end position (not included). A fourth (optional) column is reserved for the name of the interval and the sixth column (optional) is reserved for the strand. All other columns are ignored, but can be present in the file.



The display of a bed file differs by how many columns are provided in the file (see image above). The simplest, 3 column, format just displays blocks for each interval. The four column format displays the name of each element over each interval. If the sixth column is provided in the file then >>> or <<< will be displayed over each interval to represent strand information.

This format needs to be compressed by bgzip and indexed by tabix for submission as a track. See Prepare track files.


The refbed format files allows you to upload a custom gene annotation track. It is similar to the refGene bed-like file downloaded from UCSC but with slight modifications. Each file of this format contains (each column is separated by Tab):

chr, transcript_start, transcript_stop, translation_start, translation_stop, strand, gene_name, transcript_id, type, exon(including UTR bases) starts, exon(including UTR bases) stops, and additional gene info (optional)

This format needs to be compressed by bgzip and indexed by tabix for submission as a track. See Prepare track files.


The 9th column contains gene type, but is simplified from the Gencode/Ensembl annotations to coding, pseudo, nonCoding, problem, and other. These classes of gene type are colored differently when the track is displayed on the browser.


The 10th and 11th columns contain exon starts and ends respectively. Each start or end is seperated by a comma.

For example:

start1,start2,start3,start4 stop1,stop2,stop3,stop4
100,120,140,160 110,130,150,170


The 12th column contains extra information. This information can be manually annotated or we suggest using Ensembl Biomart to download paired Transcript stable IDs and Gene descriptions. The information in this column must be seperated by spaces and not tabs.

All of the below lines will work for additional information in the 12th column:

Gene ID:ENSMUSG00000103482.1 Gene Type:TEC Transcript Type:TEC Additional Info:predicted gene, 37999 [Source:MGI Symbol;Acc:MGI:5611227]
Gene ID:ENSMUSG00000103482.1 Gene Type:TEC Transcript Type:TEC
ENSMUSG00000103482.1 TEC
Additional Info:predicted gene, 37999 [Source:MGI Symbol;Acc:MGI:5611227]
My Favorite Gene

Here are a few example lines in refbed format from gencode.vM17.annotation.gtf (mouse mm10 format):

chr1        24910461        24911659        24910461        24911659        -       RP23-109H7.1    ENSMUST00000187022.1    pseudo  24911220,24910461       24911659,24910681       Gene       ID:ENSMUSG00000100808.1 Gene Type:processed_pseudogene Transcript Type:processed_pseudogene Additional Info:predicted gene 28594           [Source:MGI Symbol;Acc:MGI:5579300]
chr1        25203443        25205696        25203443        25205696        -       Adgrb3  ENSMUST00000190202.1    coding  25203443        25205696        Gene                             ID:ENSMUSG00000033569.17 Gene Type:protein_coding Transcript Type:retained_intron Additional Info:adhesion G protein-coupled receptor     B3 [Source:MGI Symbol;Acc:MGI:2441837]
chr1        25276404        25277954        25276404        25277954        -       RP23-21P2.4     ENSMUST00000193138.1    problem 25276404        25277954        Gene                         ID:ENSMUSG00000104257.1 Gene Type:TEC Transcript Type:TEC Additional Info:predicted gene, 20172 [Source:MGI Symbol;Acc:MGI:5012357]
chr1        26566833        26566938        26566833        26566938        +       Gm24064 ENSMUST00000157486.1    nonCoding       26566833        26566938        Gene                           ID:ENSMUSG00000088111.1 Gene Type:snoRNA Transcript Type:snoRNA Additional Info:predicted gene, 24064 [Source:MGI                         Symbol;Acc:MGI:5453841]


The last optional column is dislayed as a gene description when a gene is clicked on the browser. Our modified format can be easily obtained from available refGene.bed file downloads from UCSC. Gencode GTF and Ensembl GTF files can be manipulated to this format using the Converting_Gencode_or_Ensembl_GTF_to_refBed.bash script in scripts. The script by default puts Gene ID:, Gene Type:, and Transcript Type: in the additional information column. Run with an annotation file, with columns Transcript_ID and Description (seperated by a tab), the script will also add “Additional Info” to the 12th column. The script depends on bedtools, bgzip, and tabix. Lastly, within the script an awk array is used to reclassify gene type and can easily be modified for additional gene types.

The script is run as follows:

bash Converting_Gencode_or_Ensembl_GTF_to_refBed.bash Ensembl my.gtf my_optional_annotation.txt
bash Converting_Gencode_or_Ensembl_GTF_to_refBed.bash Gencode gencode.vM17.annotation.gtf
bash Converting_Gencode_or_Ensembl_GTF_to_refBed.bash Gencode gencode.vM17.annotation.gtf biomart_2col.txt


Spaces are used as delimiters in the GTF files so change gene names with spaces before processing.

For Example:

sed -i 's/ (1 of many)/_(1_of_many)/g' Danio_rerio.GRCz10.91.chr.gtf

Numerical Tracks

Currently there are two types of numerical tracks:


bigWig is a popular format to represent numerical values over genomic coordinates. Please check the UCSC bigWig page to learn more about this format.


bedGraph format also defines values in diffenent genomic locations. For more about the bedGraph format please check the UCSC bedGraph page.

Example lines are below:

chr12   6537598 6537599 28.80914
chr12   6537599 6537600 28.96908
chr12   6537599 6537612 -2
chr12   6537600 6537601 29.30229

Every line consists of 4 fields separated by the Tab delimiter. The fields from left to right are chromosome, start position (0-based), end position (not included), and value.


You can use negative values for reverse strand. Both positive and negative values can exist over the same coordinates (they can overlap). In bigWig format negative values can also be specified, but they cannot overlap with positive values.

This format needs to be compressed by bgzip and indexed by tabix for submission as a track. See Prepare track files.

Read Alignment BAM Tracks


The BAM format is a compressed SAM format used to store sequence alignment data. Please check the Samtools Documentation page to learn more about this format and how to manipulate these files.

Methylation tracks

Methylation experiments like MeDIP-seq or MRE-seq can use bigWig or bedGraph format for data display. For WGBS if users want to show read depth, methylation context, and methylation level then the data is best suited for the methylC format, described below.


Methylation data are formatted in methylC format, which is a 7 column bed format file:

chr1    10542   10543   CG      0.923   -       26
chr1    10556   10557   CHH     0.040   -       25
chr1    10562   10563   CG      0.941   +       17
chr1    10563   10564   CG      0.958   -       24
chr1    10564   10565   CHG     0.056   +       18
chr1    10566   10567   CHG     0.045   -       22
chr1    10570   10571   CG      0.870   +       23
chr1    10571   10572   CG      0.913   -       23

Each line contains 7 fields separated by Tab. The fields are chromosome, start position (0-based), end position (not included), methylation context (CG, CHG, CHG etc.), methylation value, strand, and read depth.

This format needs to be compressed by bgzip and indexed by tabix for submission as a track. See Prepare track files.

Categorical tracks

Categorical tracks represent genomic bins for different categories. The most popular example is the represnetation of chromHMM data which indicates which region is likely an enhancer, likely a promoter, etc. Other uses for the track include the display of different types of methylation (DMRs, DMVs, LMRs, UMRs, etc.) or even peaks colored by tissue type.


The categorical track uses the first three columns of the standard bed format (chromosome, start position (0-based), and end position (not included)) with the addition of a 4th column indicating the category type which can be a string or number:

chr1    start1  end1    category1
chr2    start2  end2    category2
chr3    start3  end3    category3
chr4    start4  end4    category4


when you use numbers like 1, 2 and 3 as category names, in the datahub definition, please use it a string for the category attribute in options, see the example below:

    "type": "categorical",
    "name": "ChromHMM",
    "url": "",
    "options": {
        "category": {
            "1": {"name": "Active TSS", "color": "#ff0000"},
            "2": {"name": "Flanking Active TSS", "color": "#ff4500"},
            "3": {"name": "Transcr at gene 5' and 3'", "color": "#32cd32"}

This format needs to be compressed by bgzip and indexed by tabix for submission as a track. See Prepare track files.

Long range chromatin interaction

Long range chromatin interaction data are used to show relationships between genomic regions. HiC is used to show the results from a HiC experiment.


To learn more about the HiC format please check


The longrange track is a bed format-like file type. Each row contains columns from left to right: chromosome, start position (0-based), and end position (not included), interaction target in this format chr2:333-444,55. As an example, interval “chr1:111-222” interacts with interval “chr2:333-444” on a score of 55, we will use following two lines to represent this interaction:

chr1    111 222  chr2:333-444,55
chr2    333 444  chr1:111-222,55


Be sure to make TWO records for a pair of interacting loci, one record for each locus.

This format needs to be compressed by bgzip and indexed by tabix for submission as a track. See Prepare track files.


The bigInteract format from UCSC can also be used at the browser, for more details about this format, please check the UCSC bigInteract format page.


Thanks to the higlass team who provides the data API, the browser is able to display cool tracks by using the data uuid from the higlass server, for example, you can use the uuid Hyc3TZevQVm3FcTAZShLQg to represent the track for Aiden et al. (2009) GM06900 HINDIII 1kb, for a full list of available cool tracks please check